The board of directors (the “Board”) of Atkore Inc. (“Atkore” or the “Company”), a Delaware corporation, unanimously approved an Agreement and Plan of Merger, dated as of August 2, 2026 (as it may be amended from time to time, the “Merger Agreement”), by and among Atkore, Prysmian S.p.A., a company organized under the laws of the Republic of Italy (“Prysmian”), Trinity Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of Prysmian (“Merger Sub”), and, solely as provided in certain sections of the Merger Agreement, Prysmian Cables and Systems USA, LLC, a Delaware limited liability company (“Guarantor”).

Pursuant to the Merger Agreement, at the effective time of the Merger (as defined herein) (the “Effective Time”), Merger Sub will merge with and into Atkore, with Atkore surviving as a wholly owned subsidiary of Prysmian (the “Merger”). At the Effective Time, each share of Atkore’s common stock, par value $0.01 per share (the “Common Stock”), issued and outstanding immediately prior to the Effective Time (other than shares of Common Stock to be canceled for no consideration or converted in accordance with the Merger Agreement or as to which appraisal rights have been properly exercised) will be converted into the right to receive an amount in cash equal to $95.00, without interest and subject to applicable withholding taxes (the “Merger Consideration”).

At a special meeting of Atkore stockholders (the “Special Meeting”) to be held on    , 2026, Atkore stockholders will be asked to vote on a proposal to adopt the Merger Agreement (the “Merger Proposal”). Approval of the Merger Proposal requires the affirmative vote of the holders of a majority of the outstanding shares of Common Stock as of 5:00 p.m. Eastern Time on    , 2026, the record date for the Special Meeting (the “Record Date”).

At the Special Meeting, Atkore stockholders will also be asked to approve, on an advisory (non-binding) basis, the compensation that will or may be paid or become payable to Atkore’s named executive officers in connection with the completion of the Merger (the “Compensation Proposal”), and to approve the adjournment of the Special Meeting to a later date or dates, if necessary or appropriate, to solicit additional proxies if a quorum is not present or in the event that there are not sufficient votes at the time of the Special Meeting to approve the Merger Proposal (the “Adjournment Proposal”). Assuming a quorum is present, approval of the Compensation Proposal on an advisory (non-binding) basis requires the affirmative vote of the holders of a majority of the shares of Common Stock present virtually or represented by proxy at the Special Meeting and entitled to vote on the proposal. Approval of the Adjournment Proposal requires the affirmative vote of the holders of a majority of the shares of Common Stock present virtually or represented by proxy at the Special Meeting, whether or not a quorum is present.

The Board has unanimously (i) determined that the terms of the Merger Agreement and the transactions contemplated thereby, including the Merger, are fair to, and in the best interests of, Atkore and its stockholders; (ii) determined that it is in the best interests of Atkore and its stockholders and declared it advisable to enter into the Merger Agreement; (iii) approved the execution and delivery by Atkore of the Merger Agreement, the performance by Atkore of its covenants and agreements contained therein and the consummation of the transactions contemplated by the Merger Agreement, including the Merger, upon the terms and subject to the conditions set forth therein; (iv) resolved to recommend that the stockholders of Atkore approve the Merger and adopt the Merger Agreement; and (v) directed that the Merger Agreement be submitted to the stockholders of Atkore for its adoption.

The Board unanimously recommends that the holders of shares of Common Stock vote “FOR” the Merger Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

The Record Date is 5:00 p.m. Eastern Time on    , 2026. Your vote is very important, regardless of the number of shares of Common Stock you own.

Approval of the Merger Proposal is a condition to the completion of the Merger. If the Merger Proposal is not approved, the Merger will not be completed. Approval of the Compensation Proposal and the Adjournment Proposal are not conditions to the completion of the Merger, and the votes of Atkore stockholders on the Compensation Proposal and the Adjournment Proposal will not have any bearing on whether the Merger is consummated.

Atkore will hold the Special Meeting solely by means of remote communication via the internet. All holders of record of shares of Common Stock as of the Record Date will be able to attend, vote and participate in the Special Meeting by remote communication. Whether or not you expect to attend the Special Meeting, please vote or otherwise submit a proxy to vote your shares as promptly as possible so that your shares may be represented and voted at the Special Meeting. Record holders of shares of Common Stock may submit a proxy to vote their shares of Common Stock in advance of the Special Meeting by any of the following means, as instructed on your proxy card:

The failure to vote your shares of Common Stock will have the same effect as voting “AGAINST” the approval of the Merger Proposal.

If your shares of Common Stock are held in “street name” by your bank, brokerage firm or other nominee, your bank, brokerage firm or other nominee will not be permitted to vote your shares of Common Stock without instructions from you. You should instruct your bank, brokerage firm or other nominee on how to vote your shares of Common Stock in accordance with the procedures provided by your bank, brokerage firm or other nominee. The failure to instruct your bank, brokerage firm or other nominee to vote your shares of Common Stock will have the same effect as voting “AGAINST” the approval of the Merger Proposal.

Submitting a proxy will not prevent you from attending the Special Meeting and voting virtually, and it will help to secure a quorum and avoid added solicitation costs. Any record holder of Common Stock entitled to vote at the Special Meeting and who is present at the Special Meeting may vote virtually, thereby revoking any previous proxy. Record holders of shares of Common Stock entitled to vote at the Special Meeting may also revoke their proxy in writing at any time before the Special Meeting in the manner described in the accompanying proxy statement. If your shares of Common Stock are held in “street name” by your bank, brokerage firm or other nominee, the foregoing instructions do not apply to you, and you must follow the instructions on the enclosed voting instruction card furnished by your bank, brokerage firm or other nominee to revoke your proxy.

The obligations of Prysmian and Atkore to complete the Merger are subject to the satisfaction or waiver of several conditions. The accompanying proxy statement contains detailed information about Prysmian, Atkore, the Special Meeting, the Merger Agreement, the Merger and the other transactions contemplated by the Merger Agreement. We encourage you to read the proxy statement carefully and in its entirety before voting.

On behalf of the Board and the management of Atkore, we thank you for your support.

The accompanying proxy statement is dated    , 2026 and, together with the enclosed proxy card, is first being mailed to Atkore stockholders on or about    , 2026.

We are pleased to invite you to attend the special meeting (the “Special Meeting”) of stockholders of Atkore Inc. (“Atkore”). Atkore will hold the Special Meeting solely by means of remote communication via the internet. The Special Meeting will be held on    , 2026, at     Eastern Time, virtually at www.virtualshareholdermeeting.com/ATKR2026SM for the following purposes:

Atkore will transact no other business at the Special Meeting. Please refer to the accompanying proxy statement of which this notice is a part for further information with respect to the business to be transacted at the Special Meeting.

The board of directors of Atkore (the “Board”) has fixed 5:00 p.m. Eastern Time on    , 2026 as the record date for the Special Meeting (the “Record Date”). Only holders of record of shares of Atkore’s common stock, par value $0.01 per share (“Common Stock”), on the Record Date are entitled to notice of and vote at the Special Meeting or at any adjournment or postponement thereof. A complete list of stockholders entitled to vote at the Special Meeting will be available at the executive offices of Atkore at 16100 South Lathrop Avenue, Harvey, IL 60426 for inspection by any Atkore stockholder for any purpose germane to the Special Meeting during ordinary business hours for the 10 days preceding the Special Meeting. The list will also be available for examination by stockholders during the Special Meeting at www.virtualshareholdermeeting.com/ATKR2026SM.

The Board has unanimously (i) determined that the terms of the Merger Agreement and the transactions contemplated thereby, including the Merger, are fair to, and in the best interests of, Atkore and its stockholders; (ii) determined that it is in the best interests of Atkore and its stockholders and declared it advisable to enter into the Merger Agreement; (iii) approved the execution and delivery by Atkore of the Merger Agreement, the performance by Atkore of its covenants and agreements contained therein and the consummation of the transactions contemplated by the Merger Agreement, including the Merger, upon the terms and subject to the conditions set forth therein; (iv) resolved to recommend that the stockholders of Atkore approve the Merger and adopt the Merger Agreement; and (v) directed that the Merger Agreement be submitted to the stockholders of Atkore for its adoption.

The Board unanimously recommends that the holders of shares of Common Stock vote “FOR” the Merger Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

The Record Date is 5:00 p.m. Eastern Time on    , 2026. Your vote is very important, regardless of the number of shares of Common Stock you own. Approval of the Merger Proposal is a condition to the completion of the Merger. If the Merger Proposal is not approved, the Merger will not be completed. Approval of the Compensation Proposal and the Adjournment Proposal are not conditions to the completion of the Merger, and the votes of Atkore stockholders on the Compensation Proposal and the Adjournment Proposal will not have any bearing on whether the Merger is consummated.

Whether or not you expect to attend the Special Meeting, please vote or otherwise submit a proxy to vote your shares as promptly as possible so that your shares may be represented and voted at the Special Meeting. Record holders of shares of Common Stock may submit a proxy to vote their shares of Common Stock in advance of the Special Meeting by any of the following means, as instructed on your proxy card:

The failure to vote your shares of Common Stock will have the same effect as voting “AGAINST” the approval of the Merger Proposal.

If your shares of Common Stock are held in “street name” by your bank, brokerage firm or other nominee, your bank, brokerage firm or other nominee will not be permitted to vote your shares of Common Stock without instructions from you. You should instruct your bank, brokerage firm or other nominee on how to vote your shares of Common Stock in accordance with the procedures provided by your bank, brokerage firm or other nominee. The failure to instruct your bank, brokerage firm or other nominee to vote your shares of Common Stock will have the same effect as voting “AGAINST” the approval of the Merger Proposal.

The enclosed proxy statement provides a detailed description of the Merger, the Merger Agreement and the other transactions contemplated by the Merger Agreement. We urge you to read the proxy statement carefully and in its entirety, including the annexes and the documents incorporated by reference into the proxy statement. If you have any questions concerning the Merger, the Merger Agreement, the other transactions contemplated by the Merger Agreement or the proxy statement, would like additional copies of the proxy statement or need help voting your shares of Common Stock, please contact Atkore’s proxy solicitor:

This proxy statement incorporates by reference important business and financial information about Atkore from other documents that are not included in or delivered with this proxy statement. This information is available to you without charge upon your request. You can obtain physical copies of the documents incorporated by reference into this proxy statement without charge by requesting them in writing or by telephone from our proxy solicitor at the following address and telephone numbers:

You may also consult Atkore’s website for more information about Atkore. Atkore’s website is www.atkore.com. Information contained on or connected to any website referenced in this proxy statement is not incorporated by reference into this proxy statement or in any other report or document we file with the U.S. Securities and Exchange Commission (the “SEC”), and any website references are intended to be inactive textual references only, unless expressly noted.

If you would like to request any physical copies of documents incorporated by reference into this proxy statement, please do so by    , 2026 in order to receive them before the Special Meeting.

For a more detailed description of the documents incorporated by reference into this proxy statement and how you may obtain them, see “Where You Can Find More Information.”

This proxy statement constitutes a proxy statement for Atkore under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and notice of meeting with respect to the Special Meeting of stockholders of Atkore.

You should rely only on the information contained in or incorporated by reference into this proxy statement. No one has been authorized to provide you with information that is different from that contained in, or incorporated by reference into, this proxy statement. This proxy statement is dated     , 2026. You should not assume that the information contained in this proxy statement is accurate as of any date other than that date. You should not assume that the information incorporated by reference into this proxy statement is accurate as of any date other than the date of the incorporated document. Our mailing of this proxy statement to Atkore stockholders will not create any implication to the contrary.

Information contained in this proxy statement regarding Atkore has been provided by Atkore, and information contained in this proxy statement regarding Prysmian, Merger Sub and Guarantor has been provided by Prysmian.

Unless otherwise indicated or as the context otherwise requires, as used in this proxy statement:

The following are some questions that you, as an Atkore stockholder, may have regarding the Merger and the other matters being considered at the Special Meeting, and the answers to those questions. Atkore urges you to carefully read the remainder of this proxy statement, including the documents incorporated by reference herein and the annexes attached to this proxy statement, in its entirety because the information in this section does not provide all of the information that might be important to you with respect to the Merger Agreement, the Merger and the other matters being considered at the Special Meeting. Important qualifications with respect to the representations, warranties, covenants and agreements included in the Merger Agreement are set forth in the section of this proxy statement titled “The Merger Agreement.”

Certain statements in this proxy statement and the other documents referenced herein constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, including statements regarding the benefits of the Merger and the other transactions contemplated by the Merger Agreement, future financial and operating results, objectives, expectations and intentions, and other statements that are not historical facts. Words such as “believe,” “expect,” “may,” “will,” “shall,” “should,” “would,” “could,” “seek,” “aim,” “project,” “intend,” “plan,” “estimate,” “anticipate” and similar terms, among other terms of similar substance used in connection with any discussion of future operating or financial performance, identify forward-looking statements. Where, in any forward-looking statement, we express an expectation or belief as to future results or events, such expectation or belief is expressed in good faith and believed to have a reasonable basis, but there can be no assurance that the expectation or belief will result or be accomplished. These forward-looking statements include, without limitation, statements regarding the expected completion and timing of the Merger and other information relating to the transactions contemplated by the Merger Agreement, including the Merger, as well as statements reflecting the expectations and beliefs of the Board and Atkore’s management. Important factors that could cause actual results and outcomes to differ materially from those in the forward-looking statements include, but are not limited to, the factors summarized below:

Forward-looking statements are subject to various risks and uncertainties that change over time, are based on management’s expectations and assumptions at the time the statements are made and are not guarantees of future results.

The foregoing review of important factors related to the Merger or the other transactions contemplated by the Merger Agreement should not be construed as exhaustive and should be read in conjunction with the other cautionary statements that are included herein and elsewhere.

Actual outcomes and results may differ materially from what is expressed in our forward-looking statements and from our historical financial results due to the factors discussed in this section and elsewhere in this proxy statement or disclosed in our other SEC filings. These forward-looking statements and such risks, uncertainties, and other factors speak only as of the date of this proxy statement, and Atkore expressly disclaims any obligation or undertaking to disseminate any updates or revisions to any forward-looking statement contained herein, to reflect any change in expectations with regard thereto, or any other change in events, conditions or circumstances on which any such statement is based, except to the extent required by applicable law. All subsequent written and oral forward-looking statements attributable to Atkore and/or any person acting on behalf of Atkore are expressly qualified in their entirety by this paragraph. The information contained on any websites referenced in this proxy statement or in Atkore’s periodic reports filed with the SEC is not incorporated by reference into this proxy statement.

Atkore, a Delaware corporation, is a leading manufacturer of Electrical products primarily for the non-residential construction and renovation markets, as well as residential markets, and Safety & Infrastructure products for the construction and industrial markets. The Electrical segment manufactures high quality products used in the construction of electrical power systems including conduit, cable and installation accessories. The Safety & Infrastructure segment designs and manufactures solutions including metal framing, mechanical pipe, perimeter security and cable management for the protection and reliability of critical infrastructure.

Shares of Common Stock trade on the NYSE under the symbol “ATKR.” Atkore’s principal executive offices are located at 16100 South Lathrop Avenue, Harvey, IL 60426, and Atkore’s telephone number is (708) 339-1610.

Additional information regarding Atkore is contained in our filings with the SEC, copies of which may be obtained without charge by following the instructions in the section titled “Where You Can Find More Information.”

Prysmian, a company organized under the laws of the Republic of Italy, is a leading provider of solutions for energy and digital connections, delivering major electrical transmission projects on land and at sea, modernizing power grids and unlocking renewable energy, electrification and digital connectivity worldwide. The company combines engineering excellence with sustainability-driven innovation, enabled by its 34,000 employees, 109 production facilities and 30 R&D centers in over 50 countries.

Prysmian’s ordinary shares, without nominal value, trade on the Italian Stock Exchange under the symbol “PRY.” Prysmian’s principal executive offices are located at Via Chiese 6, 20126 Milan, Italy, and Prysmian’s telephone number is +39 02 6449.1.

Merger Sub, a Delaware corporation and wholly owned subsidiary of Prysmian, was formed for the sole purpose of acquiring Atkore, including by effecting the Merger, and conducts no other business. Pursuant to the Merger Agreement, at the Effective Time, Merger Sub will merge with and into Atkore, with Atkore surviving as a wholly owned subsidiary of Prysmian.

Merger Sub’s principal executive offices are located at 4 Tesseneer Drive, Highland Heights, KY 41076, and Merger Sub’s telephone number is (859) 572-8000.

Guarantor, a Delaware limited liability company and wholly owned subsidiary of Prysmian, is a party to the transaction solely as provided in certain sections of the Merger Agreement.

Guarantor’s principal executive offices are located at 4 Tesseneer Drive, Highland Heights, KY 41076, and Guarantor’s telephone number is (859) 572-8000.

This proxy statement is being provided to holders of shares of Common Stock as part of a solicitation of proxies by the Board for use at the Special Meeting to be held at the time and place specified below and at any properly convened meeting following an adjournment or postponement thereof. This proxy statement provides holders of shares of Common Stock with information they need to know to be able to vote or instruct their vote to be cast at the Special Meeting.

Atkore will hold the Special Meeting solely by means of remote communication via the internet. The Special Meeting will be held on    , 2026, at     Eastern Time, virtually at www.virtualshareholdermeeting.com/ATKR2026SM. In order to attend the Special Meeting and vote electronically during the Special Meeting, holders of record of shares of Common Stock as of the Record Date will need the 16-digit control number found on the enclosed proxy card.

Any beneficial holders that hold their shares of Common Stock in “street name” by a bank, brokerage firm or other nominee who do not have a 16-digit control number and want to attend the Special Meeting should follow the instructions provided on the voting instruction form provided by their broker, bank or other nominee. Such holders that wish to vote at the Special Meeting must obtain a legal proxy executed in their favor from their bank, broker or other nominee prior to the Special Meeting and submit such legal proxy at the Special Meeting in order to vote virtually at the Special Meeting.

At the Special Meeting, holders of shares of Common Stock entitled to vote at the Special Meeting will be asked to consider and vote on the Merger Proposal, the Compensation Proposal and the Adjournment Proposal.

Approval of the Merger Proposal is a condition to the completion of the Merger. If the Merger Proposal is not approved, the Merger will not be completed. Approval of the Compensation Proposal and the Adjournment Proposal are not conditions to the completion of the Merger, and the votes of Atkore stockholders on the Compensation Proposal and the Adjournment Proposal will not have any bearing on whether the Merger is consummated.

On August 2, 2026, the Board unanimously (i) determined that the terms of the Merger Agreement and the transactions contemplated thereby, including the Merger, are fair to, and in the best interests of, Atkore and its stockholders; (ii) determined that it is in the best interests of Atkore and its stockholders and declared it advisable to enter into the Merger Agreement; (iii) approved the execution and delivery by Atkore of the Merger Agreement, the performance by Atkore of its covenants and agreements contained therein and the consummation of the transactions contemplated by the Merger Agreement, including the Merger, upon the terms and subject to the conditions set forth therein; (iv) resolved to recommend that the stockholders of Atkore approve the Merger; and (v) adopt the Merger Agreement and directed that the Merger Agreement be submitted to the stockholders of Atkore for its adoption.

Accordingly, the Board unanimously recommends that the holders of shares of Common Stock vote “FOR” the Merger Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

Atkore stockholders should carefully read this proxy statement, including its annexes and the documents incorporated by reference, in their entirety for more detailed information concerning the Merger and the other transactions contemplated by the Merger Agreement.

The Record Date for the Special Meeting is 5:00 p.m. Eastern Time on     , 2026. Only record holders of shares of Common Stock as of the Record Date are entitled to notice of and vote at the Special Meeting or at any adjournment or postponement thereof. As of the Record Date,       shares of Common Stock were outstanding. A list of stockholders of record who are entitled to vote at the Special Meeting will be available at the executive offices of Atkore at 16100 South Lathrop Avenue, Harvey, IL 60426 for inspection by any Atkore stockholder for any purpose germane to the Special Meeting during ordinary business hours for the 10 days preceding the Special Meeting. The list will also be available for examination by stockholders during the Special Meeting at www.virtualshareholdermeeting.com/ATKR2026SM.

Each share of Common Stock outstanding on the Record Date is entitled to one vote on each proposal and any other matter coming before the Special Meeting.

As of the Record Date, Atkore directors and executive officers were entitled to vote      shares of Common Stock, or approximately     % of the total number of shares of Common Stock outstanding at that time.

Atkore currently expects that Atkore directors and executive officers will vote all of their respective shares of Common Stock “FOR” the Merger Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

No business may be transacted at the Special Meeting unless a quorum is present. The holders of record of a majority of the outstanding shares of Common Stock as of the Record Date, present virtually or represented by proxy, will constitute a quorum for the transaction of business at the Special Meeting. Shares for which valid proxies are delivered or that are held of record by an Atkore stockholder who attends the Special Meeting virtually will be considered part of the quorum. In addition, if your shares of Common Stock are held in “street name” by your bank, brokerage firm or other nominee and you obtain a “legal proxy” executed in your favor from your bank, brokerage firm or other nominee, attend the Special Meeting virtually and submit such “legal proxy” at the Special Meeting, your shares will be considered part of the quorum. Once a share is represented for any purpose at the Special Meeting, it is deemed present for quorum purposes for the remainder of the Special Meeting and for any adjourned Special Meeting. All shares of Common Stock represented and entitled to vote at the Special Meeting, including shares of Common Stock that are represented by proxy but that vote to abstain, will be treated as present for purposes of determining the presence or absence of a quorum.

If a quorum is not present virtually or represented, or if a quorum is present virtually or represented but there are not sufficient votes at the time of the Special Meeting to approve the Merger Proposal, the Special Meeting may be adjourned by the vote of a majority of the shares of Common Stock present virtually or represented by proxy at the Special Meeting, subject to the prior written consent of Prysmian in certain circumstances, as required by the Merger Agreement. The Special Meeting may also be adjourned by the chairperson of the meeting. See “—Adjournments.” No notice of an adjourned meeting need be given if the date, time and place, if any, and the means of remote communication, if any, by which stockholders and proxyholders may be deemed to be present in person and vote at such meeting are (a) announced at the Special Meeting, (b) displayed, during the time scheduled for the Special Meeting, on the same electronic network used to enable stockholders and proxyholders to participate in the Special Meeting or (c) set forth in the notice of the Special Meeting, unless the adjournment is for more than 30 days or, after the adjournment, a new record date is fixed for the adjourned meeting, in which case notice of the adjourned meeting will be given to each stockholder of record entitled to vote at the meeting. At any adjourned meeting, any business may be transacted that might have been transacted at the original meeting. All proxies will be voted in the same manner as they would have been voted at the original convening of the Special Meeting, except for any proxies that have been effectively revoked or withdrawn prior to the adjourned meeting.

Shares of Common Stock held in “street name” for which a bank, brokerage firm or other nominee receives no instructions regarding how to vote on any of the proposals at the Special Meeting will be treated as absent for purposes of determining the presence or absence of a quorum. Shares of Common Stock held in “street name” for which a bank, brokerage firm or other nominee receives instructions regarding how to vote on some but not all of the proposals at the Special Meeting will be treated as present for determining the presence or absence of a quorum.

The required votes to approve the Atkore proposals are as follows:

If you properly complete and sign your proxy card but do not indicate how your shares of Common Stock should be voted on a proposal, the shares of Common Stock represented by your proxy will be voted in accordance with the recommendation of the Board, which is “FOR” the Merger Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

If you were a record holder of Common Stock as of the Record Date, a proxy card is enclosed for your use. Atkore requests that you submit your proxy as promptly as possible by (i) accessing the internet site listed on the proxy card, (ii) calling the toll-free number listed on the proxy card or (iii) submitting your proxy card by mail by using the provided self-addressed, stamped envelope. Information and applicable deadlines for submitting a proxy via the internet or by telephone are set forth on the enclosed proxy card. When the accompanying proxy is returned properly executed, the shares of Common Stock represented by it will be voted at the Special Meeting or at any adjournment or postponement thereof in accordance with the instructions contained in the proxy card. Your internet or telephone submission authorizes the named proxies to vote your shares in the same manner as if you had marked, signed and returned a proxy card by mail.

If a proxy is returned without an indication as to how the shares of Common Stock represented are to be voted with regard to a particular proposal, the Common Stock represented by the proxy will be voted in accordance with the recommendation of the Board, which is “FOR” the Merger Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

As of the date of this proxy statement, the Board does not know of any matters that will be presented for consideration at the Special Meeting, other than as described in this proxy statement, and, in accordance with the Merger Agreement, Atkore has agreed that, without the prior written consent of Prysmian, other than as described in this proxy statement, no other matters will be considered at the Special Meeting (other than matters of procedure and matters required by applicable law to be voted on by Atkore stockholders in connection therewith and the transactions contemplated by the Merger Agreement). If any other matter properly comes before the Special Meeting, or at any adjournment or postponement of the Special Meeting, and is voted upon, the enclosed proxy card will confer discretionary authority to the individuals named as authorized therein to vote the shares represented by the proxy as to any such matters. It is intended that the persons named in the enclosed proxy card and acting thereunder will vote in accordance with their best judgment on such matters.

Your vote is very important, regardless of the number of shares of Common Stock you own. Accordingly, if you were a record holder of Common Stock as of the Record Date, please submit your proxy via the internet or telephone or sign and return the enclosed proxy card as promptly as possible, regardless of whether you expect to attend the Special Meeting. Proxies submitted through the specified internet website or by phone must be received by 11:59 p.m. Eastern Time on      , 2026, the day before the Special Meeting. You can subsequently change your vote, as described herein.

If you hold shares of Common Stock through a bank, brokerage firm or other nominee, you are considered the “beneficial holder” of the shares held for you in what is known as “street name.” The “record holder” of such shares is your bank, brokerage firm or other nominee, and not you, and you must provide the record holder of your shares of Common Stock with instructions on how to vote your shares. Please follow the voting instructions provided by your bank, brokerage firm or other nominee so that it may vote your shares on your behalf. Please note

that you may not vote shares of Common Stock held in street name by returning a proxy card directly to Atkore, and if you do not have a 16-digit control number, you may not vote shares of Common Stock held in street name by voting virtually at the Special Meeting, unless you first obtain a “legal proxy” executed in your favor from your bank, brokerage firm or other nominee and submit such “legal proxy” at the Special Meeting. Furthermore, banks, brokerage firms or other nominees who hold shares of Common Stock on behalf of their customers may not give a proxy to Atkore to vote those shares without specific instructions from their customers.

If you hold shares of Common Stock in “street name” through a bank, brokerage firm or other nominee, and you do not instruct your bank, brokerage firm or other nominee on how to vote your shares, your bank, brokerage firm or other nominee will not vote your shares on any of the proposals to be considered at the Special Meeting. The failure to instruct your bank, brokerage firm or other nominee to vote your shares of Common Stock will have the same effect as voting “AGAINST” the approval of the Merger Proposal.

All holders of shares of Common Stock as of the Record Date, including record holders of shares of Common Stock and beneficial owners of Common Stock registered in the “street name” of a bank, brokerage firm or other nominee will be able to attend the Special Meeting.

Record holders of shares of Common Stock will be able to vote virtually at the Special Meeting. In order to attend the Special Meeting and vote electronically during the Special Meeting, holders of record of shares of Common Stock as of the Record Date will need the 16-digit control number found on the enclosed proxy card. If you are not a record holder of Common Stock but instead hold your shares of Common Stock in “street name” through a bank, brokerage firm or other nominee and you do not have a 16-digit control number, you must obtain a legal proxy executed in your favor from your bank, brokerage firm or other nominee and submit such “legal proxy” at the Special Meeting in order to be able to vote virtually at the Special Meeting.

To ensure that your shares of Common Stock are represented at the Special Meeting, we recommend that you provide voting instructions promptly by proxy, even if you plan to attend the Special Meeting virtually. You can subsequently change your vote, as described herein.

If you are the record holder of Common Stock, you can change your vote or revoke your proxy at any time before your proxy is exercised at the Special Meeting. You can do this by:

A record holder of Common Stock may change their vote or revoke their proxy by any of these methods, regardless of the method used to deliver the stockholder’s previous proxy.

Written notices of revocation and other communications with respect to the revocation of proxies should be addressed to Atkore as follows:

If your shares are held in “street name” through a bank, brokerage firm or other nominee, you may change your voting instructions by submitting new voting instructions to your bank, brokerage firm or other nominee in accordance with its established procedures. If your shares are held in the name of a bank, brokerage firm or other nominee and you do not have a 16-digit control number and decide to change your vote by attending the Special Meeting virtually and voting at the Special Meeting, your vote at the Special Meeting will not be effective, unless you have obtained a legal proxy executed in your favor from the record holder (your bank, brokerage firm or nominee) and submit such “legal proxy” at the Special Meeting.

Once voting on a particular matter is completed at the Special Meeting, an Atkore stockholder will not be able to revoke its proxy or change its vote as to that matter.

Atkore expects to appoint Broadridge to serve as the inspector of election for the Special Meeting. The inspector of election will, among other matters, determine the number of shares of Common Stock entitled to vote at the Special Meeting that are represented at the Special Meeting to confirm the existence of a quorum for the Special Meeting, determine the validity of all proxies and ballots and certify the results of voting on the Merger Proposal, the Compensation Proposal and the Adjournment Proposal submitted to stockholders.

Atkore is soliciting proxies for the Special Meeting from holders of shares of Common Stock. In addition to solicitation of proxies by mail, proxies may be solicited by Atkore’s directors, officers, employees and certain other representatives, without additional compensation, in person, by telephone, email or other means of communication.

Atkore will make arrangements with banks, brokerage firms and other intermediaries and fiduciaries to forward proxy solicitation materials to beneficial owners of Common Stock. We may reimburse these banks, brokerage firms and other intermediaries and fiduciaries for their reasonable expenses in forwarding proxy materials to the beneficial owners.

Atkore has engaged Innisfree to solicit proxies on Atkore’s behalf and provide consulting and analytic services in connection with the Special Meeting. Atkore expects to pay Innisfree a fee of approximately $45,000, plus a success fee of $22,500, for these services. Atkore will also reimburse Innisfree for certain fees and expenses associated with its services and has agreed to indemnify Innisfree for certain losses relating to or arising out of Innisfree’s services.

The Special Meeting may be adjourned by the vote of a majority of the shares of Common Stock present virtually or represented by proxy at the Special Meeting on one or more occasions for the purpose of soliciting additional proxies, if there is an insufficient number of shares of Common Stock present (either virtually or by proxy) to constitute a quorum or an insufficient number of shares of Common Stock have been voted virtually or by proxy in favor of the approval of the Merger Proposal, subject to the prior written consent of Prysmian in certain circumstances, as required by the Merger Agreement. In addition, the Special Meeting may be adjourned by the chairperson of the meeting. Atkore may, without Prysmian’s prior written consent, adjourn or postpone the Special Meeting (i) if Atkore believes in good faith that such adjournment or postponement is reasonably necessary to allow reasonable additional time to (A) solicit additional proxies necessary to obtain approval of the Merger Proposal or (B) distribute any supplement or amendment to this proxy statement, the distribution of which the Board has determined in good faith to be necessary under applicable law, or (ii) for an absence of a quorum, in which case Atkore will use its reasonable best efforts to obtain a quorum as promptly as practicable. Atkore may not, without Prysmian’s prior written consent, adjourn or postpone the Special Meeting more than a total of three times for purposes of soliciting additional proxies necessary to obtain approval of the Merger Proposal or for an absence of a quorum, and no such adjournment or postponement may exceed ten days or thirty days in the aggregate. At any adjourned meeting, any business may be transacted that might have been transacted at the original meeting. All proxies will be voted in the same manner as they would have been voted at the original convening of the Special Meeting, except for any proxies that have been effectively revoked or withdrawn prior to the adjourned meeting. See “The Merger Agreement—Covenants and Agreements—Atkore Special Meeting” and “—Quorum.”

For a summary and detailed information regarding the Merger Proposal, see the information about the Merger Agreement throughout this proxy statement, including the information set forth in the sections titled “The Merger” and “The Merger Agreement.” A copy of the Merger Agreement is attached as Annex A to this proxy statement.

Stockholder approval of the Merger Proposal is a condition to the completion of the Merger. If the Merger Proposal is not approved by stockholders, the Merger will not occur.

The vote on the Merger Proposal is separate and apart from the votes to approve the Compensation Proposal and the Adjournment Proposal. Accordingly, you may vote to approve the Merger Proposal and vote not to approve either or both of the other proposals and vice versa.

The Merger Proposal requires the affirmative vote of the holders of a majority of the outstanding shares of Common Stock as of the Record Date. Abstentions from voting and failures to vote (including failure to instruct your bank, brokerage firm or other nominee on how to vote your shares of Common Stock) will have the same effect as a vote “AGAINST” the approval of the Merger Proposal.

The Board unanimously recommends that the holders of shares of Common Stock vote “FOR” the Merger Proposal.

Section 14A of the Exchange Act and the applicable SEC rules thereunder, which were implemented as part of the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010, require Atkore to provide its stockholders with the opportunity to vote to approve, on a non-binding, advisory basis, the compensation that will or may be paid or become payable to Atkore’s named executive officers in connection with the completion of the Merger, including the payments summarized in the “golden parachute compensation” table and the related narrative compensation disclosures regarding Atkore’s named executive officers set forth in “The Merger—Quantification of Potential Payments and Benefits to Atkore’s Named Executive Officers in Connection with the Merger.” Accordingly, Atkore stockholders are being provided with the opportunity to cast an advisory vote on these change-of-control payments.

As an advisory vote, the Compensation Proposal is not binding upon Atkore, the Board or the Human Resources and Compensation Committee of the Board, and approval of the Compensation Proposal is not a condition to completion of the Merger. Accordingly, if the Merger is completed, the compensation payments described in the Compensation Proposal that are contractually required to be paid or become payable to Atkore’s named executive officers will remain in place, subject only to the existing terms and conditions applicable thereto, regardless of the outcome of the advisory (non-binding) vote of Atkore stockholders on the Compensation Proposal.

Atkore is seeking approval of the following resolution at the Special Meeting:

“RESOLVED, that the stockholders of Atkore Inc. approve, on an advisory (non-binding) basis, the compensation that will or may become payable to the named executive officers of Atkore Inc. in connection with the Merger, as disclosed pursuant to Item 402(t) of Regulation S-K in “The Merger—Quantification of Potential Payments and Benefits to Atkore’s Named Executive Officers in Connection with the Merger” (which disclosure includes the ‘Golden Parachute’ Compensation table required pursuant to Item 402(t) of Regulation S-K).”

The vote on the Compensation Proposal is separate and apart from the votes to approve the Merger Proposal and the Adjournment Proposal. Accordingly, you may vote to approve the Compensation Proposal and vote not to approve either or both of the other proposals and vice versa.

Assuming a quorum is present, approval of the Compensation Proposal on an advisory (non-binding) basis requires the affirmative vote of the holders of a majority of the shares of Common Stock present virtually or represented by proxy at the Special Meeting and entitled to vote on the proposal. If you attend the Special Meeting or are represented by proxy and, in either case, abstain from voting, assuming a quorum is present, that abstention will have the same effect as voting “AGAINST” the approval of the Compensation Proposal. Assuming a quorum is present, failures to vote will have no effect on the vote for the Compensation Proposal.

The Board unanimously recommends that the holders of shares of Common Stock vote “FOR” the Compensation Proposal.

If a quorum is not present or Atkore fails to receive a sufficient number of votes to approve the Merger Proposal, Atkore may propose to adjourn the Special Meeting for the purpose of soliciting additional proxies. Atkore currently does not intend to propose adjournment of the Special Meeting if a quorum is present and there are sufficient votes to approve the Merger Proposal. Atkore does not intend to call a vote on the Adjournment Proposal if the Merger Proposal is approved at the Special Meeting.

The vote on the Adjournment Proposal is separate and apart from the votes to approve the Merger Proposal and the Compensation Proposal. Accordingly, you may vote to approve the Adjournment Proposal and vote not to approve either or both of the other proposals and vice versa.

Approval of the Adjournment Proposal requires the affirmative vote of the holders of a majority of the shares of Common Stock present virtually or represented by proxy at the Special Meeting, whether or not a quorum is present. If you attend the Special Meeting or are represented by proxy and, in either case, abstain from voting, that abstention will have the same effect as voting “AGAINST” the approval of the Adjournment Proposal. Failures to vote will have no effect on the vote for the Adjournment Proposal.

The Board unanimously recommends that the holders of shares of Common Stock vote “FOR” the Adjournment Proposal.

This section describes the Merger. The description in this section and elsewhere in this proxy statement is qualified in its entirety by reference to the complete text of the Merger Agreement, a copy of which is attached as Annex A, and which is incorporated by reference into this proxy statement. This summary does not purport to be complete and may not contain all the information about the Merger that is important to you. You are encouraged to read the Merger Agreement carefully and in its entirety. This section is not intended to provide you any factual information about Atkore. Such information can be found elsewhere in this proxy statement and in the public filings Atkore makes with the SEC, as described in the section titled “Where You Can Find More Information.”

At the Effective Time, Merger Sub will merge with and into Atkore, with Atkore surviving as a wholly owned subsidiary of Prysmian. As a result of the Merger, Prysmian will acquire Atkore.

At the Effective Time, each share of Common Stock issued and outstanding immediately prior to the Effective Time (other than shares of Common Stock to be canceled for no consideration or converted into shares of the surviving corporation in the Merger in accordance with the Merger Agreement or as to which appraisal rights have been properly exercised) will be converted into the right to receive an amount in cash equal to $95.00, without interest and subject to applicable withholding taxes.

Following the Effective Time, the Common Stock will be delisted from the NYSE and deregistered under the Exchange Act, and Atkore will no longer be required to file periodic reports with the SEC on account of the Common Stock. The completion of the Merger is subject to certain conditions. See “The Merger Agreement—Conditions to Completion of the Merger.”

If the Merger Proposal is not approved by the affirmative vote of the holders of a majority of the outstanding shares of Common Stock as of the Record Date, or if the Merger is not completed for any other reason, Atkore’s stockholders will not be entitled to, nor will they receive, any payment for their shares of Common Stock pursuant to the Merger Agreement. Instead, Atkore will remain an independent public company, the Common Stock will continue to be listed and traded on the NYSE and registered under the Exchange Act, and Atkore will continue to file periodic reports with the SEC.

Prior to the Effective Time, Atkore anticipates that management will operate the business in a manner similar to that in which it is being operated today and Atkore’s stockholders will be subject to similar risks and opportunities to which they are currently subject, including, without limitation, risks related to the highly competitive industry in which Atkore operates, the servicing of Atkore’s debt, market volatility and adverse economic conditions.

If the Merger is not completed, and depending on the circumstances that would have caused the Merger to not be completed, the price of Common Stock may decline significantly. If that were to occur, it is uncertain when, if ever, the price of Common Stock would return to the price at which it trades as of the date of this proxy statement. If the Merger Proposal is not approved by Atkore stockholders or if the Merger is not completed for any other reason, there can be no assurance that any other transaction acceptable to Atkore will be offered or that Atkore’s business, prospects or results of operation will not be adversely affected. If the Merger Agreement is terminated, under certain specified circumstances, Atkore may be required to pay the Company Termination Fee. See “The Merger Agreement—Termination of the Merger Agreement” for a discussion of the circumstances under which the Company Termination Fee may be payable.

The following chronology summarizes the material meetings and events that led to the execution of the Merger Agreement. This chronology does not purport to catalogue every conversation of, or among, the Board, members of Atkore’s senior management or Atkore’s advisors and other parties.

The Board, together with Atkore’s senior management, regularly reviews Atkore’s performance, growth prospects and overall strategic direction and evaluates potential opportunities to strengthen Atkore’s business and enhance value for its stockholders. From time to time, these reviews and evaluations have included consideration of potential strategic alternatives, including potential strategic acquisitions and divestitures and other strategic transactions.

In January 2025, representatives of a European electrical industry participant (“Bidder A”), reached out to Atkore unsolicited to express interest in exploring a potential business combination between Bidder A and Atkore. Thereafter, Mr. Waltz met with the Chief Executive Officer and other senior management of Bidder A to discuss Bidder A’s interest in Atkore.

On January 29, 2025, the Board held an in-person meeting, which included senior management of Atkore. During the meeting, the Board discussed the meeting between Mr. Waltz and the Chief Executive Officer and other senior management of Bidder A. Following this discussion, the Board requested that Atkore obtain a third-party perspective on Atkore’s intrinsic value.

On February 14, 2025, members of senior Atkore management met separately with representatives of each of Citi and J.P. Morgan to discuss Atkore’s recent financial performance and certain potential and illustrative strategic alternatives, including continuing Atkore’s existing strategy, conducting a broader strategic review and evaluating potential dispositions of non-core assets to transform Atkore into an electrical-focused portfolio business.

On March 12, 2025, members of Atkore management met with representatives of Citi to discuss Atkore’s 2025 strategic plan, perspectives on valuation, and potential strategies for future value creation, including through M&A.

On March 21, 2025, the Board held a meeting via means of remote communication, which included senior management of Atkore. During the meeting, Atkore’s general counsel presented to the Board on certain litigation matters and their potential impact on Atkore. Additionally, members of management of Atkore provided an update to the Board regarding its discussions with representatives of Citi and J.P. Morgan regarding Atkore’s recent financial performance and reviewed certain potential strategic alternatives available to Atkore.

On April 24, 2025, members of Atkore management met with representatives of Citi to discuss the potential sale of Atkore’s high-density polyethylene (“HDPE”) business. During the meeting, representatives of Citi discussed with Atkore management various considerations relating to a potential sale of the HDPE business, including the market landscape, the possible transaction structure and perimeter, potential buyers and Atkore’s financial position following a sale of the HDPE business.

On April 29, 2025, the Board held an in-person meeting, which included senior management of Atkore. During the meeting, the Board discussed Atkore management’s work undertaken with representatives of Citi and J.P. Morgan since the January 29, 2025 Board meeting, including Atkore management’s EBITDA and growth assumptions and various valuation methods and the preliminary perspectives on valuation discussed with representatives of Citi and J.P. Morgan. The Board discussed and considered a number of potential strategic options, including continuing the status quo, acquiring or divesting certain business lines, selling Atkore as a whole, or merging with a strategic partner. The Board further discussed the additional information it would need to evaluate such alternatives, including timing and tax considerations. The Board unanimously agreed to continue working with external advisors to analyze specific alternatives, including divestiture options. The Board also discussed the declining sales and increasing losses in Atkore’s HDPE business.

On July 30, 2025, the Board held an in-person meeting, which included senior management of Atkore and representatives of Citi. Representatives of Citi discussed with the Board various potential strategic alternatives, including potential alternatives for non-core assets, Atkore’s go-forward M&A strategy as well as initial considerations for addressing the possibility of stockholder activism in the current activism landscape with a view to enhancing value for Atkore’s stockholders. As part of the discussion of potential alternatives for non-core assets, the Board discussed with Atkore management and representatives of Citi the potential sale of the HDPE business in the context of the HDPE business’s deteriorating performance, including a discussion of potential negative repercussions of selling the HDPE business at a loss, as well as whether the announcement of the sale of the HDPE business might lead to offers for a whole-company transaction with Atkore or other parts of its business. The Board also discussed with Atkore management and representatives of Citi plans for the remaining business of Atkore if the HDPE business were sold, including the types of potential buyers who might be interested in Atkore as a whole. Following such discussion, the representatives of Citi departed from the meeting, and following further discussion, the Board unanimously resolved to authorize Atkore management to work with its financial advisors to contact select potential buyers of the HDPE business.

On September 9, 2025, in accordance with the Board’s authorization and following preparation work with Atkore’s management, Citi launched a sale process for Atkore’s HDPE business by contacting potential buyers.

On September 16, 2025, Atkore received a letter from Irenic Capital Evergreen Master Fund LP (“Irenic”) disclosing that Irenic had accumulated a stake in Atkore and requesting that Atkore conduct a strategic review.

On September 19, 2025, the Board held a meeting via means of remote communication, which included senior management of Atkore and representatives of Citi, Debevoise & Plimpton LLP (“Debevoise”) and Joele Frank, Wilkinson Brimmer Katcher (“Joele Frank”). At the meeting, Atkore management and representatives of Citi, Debevoise and Joele Frank discussed with the Board potential responses to Irenic’s letter. Debevoise also reviewed with the Board the directors’ fiduciary duties in connection with the matters under consideration.

On September 26, 2025, the Board held a meeting via means of remote communication, which included senior management of Atkore and representatives of Citi, Debevoise and Joele Frank. At the meeting, members of Atkore management and representatives of Citi, Debevoise and Joele Frank updated the Board regarding management’s engagement with Irenic and discussed potential responses to Irenic. Debevoise reviewed with the Board the directors’ fiduciary duties in connection with the matters under consideration.

On September 28, 2025, the Board held a meeting via means of remote communication. At this meeting, the Board approved the public announcement of a review of strategic alternatives, including a potential divestiture of the HDPE business.

On September 29, 2025, Atkore announced that it was evaluating a broad range of strategic alternatives to enhance its focus on Atkore’s core electrical infrastructure portfolio. In connection with this announcement, Atkore announced that it was reviewing select assets that might not fit its core electrical infrastructure portfolio, including a potential sale of the HDPE business. On the same date, Atkore announced other steps it was taking to reduce costs, including a reduction in headcount and the identification of three manufacturing facilities that would be consolidated in calendar year 2026.

On September 30, 2025, media sources reported that Irenic had built a 2.5% economic stake in Atkore and was advocating for a potential sale of Atkore.

On October 8, 2025, the Board held a meeting via means of remote communication, which included senior management of Atkore and representatives from Debevoise. During the meeting, the Board discussed Atkore’s September 29^th announcement regarding its review of strategic alternatives and (i) the status of the HDPE sale process, including timing and next steps and (ii) preparations for a potential broader strategic review, including considerations relating to the timing and potential launch of a formal sale process for Atkore as a whole, and the Board’s options in responding to potential unsolicited acquisition proposals.

Throughout October and early November 2025, a number of financial sponsors contacted representatives of Citi regarding Atkore, and Citi held initial discussions with certain of these parties. On October 14, 2025, one of these financial sponsors (“Bidder B”) submitted an unsolicited written preliminary proposal expressing interest in a potential acquisition of Atkore in an all-cash transaction. The preliminary proposal did not specify a proposed purchase price and contemplated that Bidder B would submit a proposal regarding valuation following completion of certain priority due diligence and management discussions.

On October 16, 2025, the Board held a meeting via means of remote communication, which included senior management of Atkore and representatives of Citi, Debevoise and Joele Frank. During the meeting, representatives of Citi updated the Board regarding recent interest in Atkore from certain financial sponsors, and the Board approved continuing the engagement with two financial sponsor parties to assess possible third-party interest in Atkore as a whole. Citi also updated the Board regarding the status of preparations for a potential sale process for Atkore as a whole, including preparation of Atkore management’s long-term strategic plan, diligence materials, marketing materials and potential buyer outreach.

On October 28, 2025, Atkore received a letter from Irenic nominating six (6) directors to the Board in advance of the 2026 annual meeting of the stockholders.

On October 30, 2025, the Board held a meeting via means of remote communication with senior management and representatives of Citi, Debevoise and Joele Frank to discuss developments relating to Irenic and the potential Atkore sale process. During this meeting, the Board also approved the engagement with a third financial sponsor party.

Between October 30 and November 3, 2025, Atkore entered into confidentiality agreements with the three financial sponsors, and Atkore and representatives of Citi continued discussions with such financial sponsors,

including by providing certain parties with marketing materials and financial information and conducting management and legal due diligence sessions. Thereafter, throughout November and December 2025 and January 2026, Atkore negotiated (through Debevoise) and entered into confidentiality agreements with various potential bidders.

On November 4 and November 10, 2025, the Board held meetings with senior management and representatives of Citi, Debevoise and Joele Frank to discuss developments relating to Irenic and the potential Atkore sale process. During these meetings, the Board received updates regarding exploratory discussions with potential acquirors and preparations for a potential sale process and considered potential terms of a resolution with Irenic, including the proposed formation of a strategic review committee and public announcement of an expanded strategic review. During the November 10, 2025 meeting, the Board authorized a framework for a potential settlement with Irenic.

On November 12, 2025, Atkore and J.P. Morgan entered into an engagement letter pursuant to which J.P. Morgan was engaged to act as co-financial advisor in connection with a potential sale of Atkore. On November 17, 2025, Atkore and Citi entered into an engagement letter, replacing and expanding the scope of Citi’s prior engagement letter with Atkore, pursuant to which, among other things, Citi was engaged to act as lead financial advisor in connection with a potential sale of Atkore.

On November 17-18, 2025, the Board held an in-person meeting, which included senior management of Atkore and representatives of Citi, J.P. Morgan and Debevoise. At the meeting, Mr. Waltz updated the Board regarding the preliminary evaluations of Atkore being conducted by the three financial sponsors and the status of discussions with Irenic regarding a potential cooperation agreement. Debevoise also reviewed with the Board the fiduciary duties of directors in connection with the evaluation of strategic alternatives. Representatives of Citi then reviewed with the Board the status of the preliminary diligence on Atkore conducted by the three financial sponsors and discussed a potential expanded strategic alternatives process, including an illustrative timeline for such a process. The Board discussed with representatives of Citi considerations relating to such potential expanded strategic process, including feedback received from the three financial sponsors that a divestiture of the HDPE business prior to the sale of Atkore as a whole would be desirable, whether additional interest in Atkore could emerge following the announcement of an expanded strategic alternatives review and how prospective acquirors might react to certain litigation and investigation matters relating to alleged anticompetitive conduct related to the price of PVC pipes sold in the United States (and separately in Canada) since 2021 or earlier, which included civil antitrust class action lawsuits (the “Antitrust Litigation”), a civil investigation demand from the Florida Attorney General and a Department of Justice investigation (together, the “Antitrust Investigation”), and securities class action lawsuits, stockholder derivative litigation, and stockholder demands on the Board (the “Stockholder Litigation” and, collectively with the Antitrust Litigation and the Antitrust Investigation, the “Antitrust and Related Matters”). Representatives of Citi also updated the Board regarding the status of Atkore’s discussions with Irenic and the Board authorized continued negotiations and settlement with Irenic, within a defined set of parameters.

On November 20, 2025, Atkore announced that it had expanded the scope of its previously announced review of strategic alternatives and would consider a broader range of alternatives to maximize stockholder value, including a potential sale or merger of Atkore. On the same date, Atkore announced that it had entered into a cooperation agreement with Irenic, pursuant to which it expanded the Board and appointed Franklin S. Edmonds as a director. Pursuant to the cooperation agreement, the Board formed a strategic review committee (the “Strategic Review Committee”), including Mr. Waltz, Mr. Schrock, Ms. Isbell and Mr. Edmonds, and Bruce Taten as special advisor to the Strategic Review Committee, to oversee, evaluate and provide advice to the Board regarding its review of strategic alternatives.

On November 20, 2025, the Chairman of the board of directors of a strategic party (“Bidder C”) and the Chairman of the Board discussed Bidder C’s interest in a potential business combination between Atkore and Bidder C.

On November 21, 2025, Citi and J.P. Morgan, on behalf of Atkore, formally launched a targeted sell-side process for Atkore as a whole by contacting potential strategic and financial buyers.

On November 21, 2025, representatives of the financial advisor of Bidder C and representatives of Citi discussed Bidder C’s interest in a potential business combination with Atkore. Through late November and early December of 2025, Bidder C and Atkore, through their respective outside counsel, negotiated the terms of a confidentiality agreement. During these negotiations, Bidder C indicated that a potential proposal could include a mix of cash and stock consideration, and requested a mutual confidentiality agreement. On December 19, 2025,

Bidder C and Atkore entered into a one-way confidentiality agreement in favor of Atkore, with the understanding that the parties could enter into a reciprocal confidentiality agreement in the future to the extent Bidder C’s proposal included stock consideration, which Atkore and Bidder C later entered into on February 19, 2026.

On November 22, 2025, Prysmian contacted representatives of Citi regarding Atkore. On November 25, 2025, during a meeting between representatives of Citi and Prysmian, representatives of Citi discussed with Prysmian the Atkore sale process, and Prysmian expressed interest in participating in the process.

Later, on November 25, 2025, representatives of Citi sent a draft confidentiality agreement to Prysmian. Between November 27 and December 3, 2025, Prysmian, through its in-house counsel, and Atkore, through Debevoise, negotiated the terms of the confidentiality agreement, which Prysmian and Atkore entered into on December 3, 2025.

On December 3, 2025, the Strategic Review Committee met by means of remote communication, with representatives of Citi and J.P. Morgan in attendance. During the meeting, the Strategic Review Committee discussed objectives of the strategic review and the status of the Atkore sale process following the announcement of the expanded strategic review. As of the date of this meeting, twenty-eight potentially interested parties had contacted Atkore’s advisors to express interest in Atkore or parts thereof. The Strategic Review Committee also discussed key considerations in the sale process, including the impact of the Antitrust and Related Matters and the potential divestiture of the HDPE business. The Strategic Review Committee’s discussion also included perspectives on Atkore’s broader capital allocation strategy.

On December 5, 2025, Bidder B submitted a non-binding indication of interest to acquire Atkore for between $72.00 and $77.00 per share in cash. The proposed price assumed no liability exposure with respect to the Antitrust and Related Matters, which remained subject to further due diligence. The proposal remained subject to completion of due diligence, negotiation of definitive documentation, final internal approval and receipt of debt financing commitments.

On December 7, 2025, representatives of Citi sent Prysmian Atkore’s confidential information presentation.

On December 19, 2025, representatives of Citi sent Prysmian Atkore’s sell-side financial model.

On December 22, 2025, the Strategic Review Committee met by means of remote communication, with representatives of Citi and J.P. Morgan in attendance, to discuss the status of the sale process. As of the date of this meeting, twenty-eight potentially interested parties had contacted Atkore or its advisors or had been contacted by them since Atkore’s November 20, 2025 announcement of the expanded strategic review process. Three parties had declined to proceed, including certain parties that cited uncertainty regarding the Antitrust and Related Matters. During the same meeting, the Strategic Review Committee also discussed the status of the HDPE divestiture, including the likely buyer and the timeline for execution of definitive transaction documents.

On December 29, 2025, representatives of Citi and J.P. Morgan, on behalf of Atkore, sent an initial process letter to participants in the Atkore sale process, requesting indications of interest by January 26, 2026.

During January 2026, Atkore and its advisors continued to provide due diligence access to seven potentially interested parties, including through management and legal due diligence sessions and site visits.

On January 15, 2026, the Strategic Review Committee met by means of remote communication, with representatives of Citi and J.P. Morgan in attendance, to discuss the status of the Atkore expanded sale process and the HDPE divestiture. During this meeting, the Strategic Review Committee discussed the status of Atkore’s engagement with potentially interested parties. The Strategic Review Committee also discussed the impact of the Antitrust and Related Matters on the potential bidders’ diligence process, including that the absence of greater definition or quantification of potential net litigation exposure could delay the Atkore sale process timeline. The Strategic Review Committee also discussed the latest developments in the HDPE divestiture process, including that Atkore was finalizing an exclusivity agreement with a potential buyer of the HDPE business.

On January 26, 2026, Atkore and its advisors received three non-binding indications of interest (the “January Bids”):

On January 28-29, 2026, the Board held an in-person meeting, which included senior management of Atkore and representatives of Citi and J.P. Morgan. At the meeting, counsel representing Atkore in connection with the Antitrust and Related Matters and Atkore’s general counsel updated the Board regarding the Antitrust Litigation, the Antitrust Investigation, and the Stockholder Litigation. During the Board meeting, a meeting of the Strategic Review Committee took place, with the rest of the Board in attendance, during which representatives of Citi reviewed the January Bids, noting that none of the January Bids took into account potential liabilities relating to the Antitrust and Related Matters. The Strategic Review Committee, with the Board in attendance, further discussed the parties that had declined to participate further in the process, and the reasons therefor, including the uncertainty regarding the magnitude of potential liabilities arising from the Antitrust and Related Matters. Certain parties indicated that they might reconsider participating if there were greater clarity regarding such matters.

In February 2026, Atkore adjusted the timing of its sale process in light of uncertainty regarding the Antitrust and Related Matters and the outcome of the HDPE sale process, and the effect of such uncertainty on bidder participation and their valuation of Atkore. Following consultation with its financial advisors, the Board determined that a process on the previously contemplated timeline would be unlikely to lead to a successful outcome, and that Atkore should continue to engage with third parties over time with the goal of accelerating the process once there was more clarity regarding the magnitude of liabilities associated with the Antitrust and Related Matters, as well as the outcome of the HDPE divestiture. Thereafter, Atkore and its advisors continued to facilitate diligence and engage with certain potential bidders, including Prysmian, Bidder C and Bidder D. During February and March 2026, this engagement included reverse diligence by Atkore with respect to Bidder C in light of the stock component of Bidder C’s proposal and additional business and operational diligence by Prysmian, including site visits and meetings with Prysmian and Bidder C’s senior management teams.

On March 10, 2026, the Strategic Review Committee held a meeting by means of remote communication, with representatives of Citi and J.P. Morgan in attendance. At the meeting, representatives of Citi and J.P. Morgan provided an update on the status of diligence by Prysmian, Bidder C and Bidder D. The Strategic Review Committee discussed the timeline for the Atkore sale process and determined to continue monitoring developments regarding the Antitrust and Related Matters and the HDPE divestiture before reassessing the process timeline.

On March 23, 2026, the Board held a meeting by means of remote communication, which included senior management of Atkore and outside counsel representing Atkore in connection with certain of the Antitrust Litigation matters. At the meeting, outside counsel and Atkore’s general counsel provided an update to the Board on the status of the In re PVC Pipe Antitrust Litigation. Later at the same meeting, members of Atkore management presented to the Board on the status of the HDPE divestiture, including tax implications of the transaction. Following a discussion, the Board approved the HDPE divestiture.

On April 1, 2026, the Board held a meeting via means of remote communication, which included senior management of Atkore. During the meeting, the Board discussed aspects of a potential settlement agreement with one of the classes of plaintiffs in the In re PVC Pipe Antitrust Litigation matter, and instructed management to continue settlement discussions.

On April 7, 2026, members of Atkore management and representatives of Prysmian met for a joint virtual session to discuss potential synergies from a potential acquisition of Atkore by Prysmian. During this session, the parties discussed, among other potential synergies, the synergies related to procurement, manufacturing and market opportunities.

On April 7, 2026, wholly owned subsidiaries of Atkore entered into definitive documentation to sell Atkore’s HDPE business. On April 8, 2026, Atkore announced the sale of the HDPE business to Infra Pipes.

On April 23, 2026, the Board held a meeting by means of remote communication, which included senior management of Atkore and outside counsel representing Atkore in connection with the Antitrust and Related Matters. At the meeting, outside counsel and Atkore’s general counsel updated the Board regarding the Antitrust Litigation, the Antitrust Investigation, and the Stockholder Litigation.

On April 28, 2026, Atkore entered into agreements, subject to court approval, to settle with two of three classes in the In re PVC Pipe Antitrust Litigation for aggregate payments of $136.5 million. Following these settlements, one putative class action litigation matter from the Antitrust Litigation, as well as other matters related to the Antitrust and Related Matters (including the Antitrust Investigation and Stockholder Litigation), remained pending.

Following developments in the Antitrust Litigation, including the April 28 settlements, and Atkore’s announcement of quarterly earnings on May 5, 2026, Atkore began increasing its engagement with potential bidders still involved in the process and re-engaged with other potential bidders which had previously stepped back from the process but had indicated a desire to re-engage if certain of the Antitrust and Related Matters were resolved. In total, ten parties were engaged in the process in May 2026, with eight potential bidders conducting diligence regarding Atkore, including business diligence sessions with management, quality of earnings diligence calls and diligence regarding the Antitrust and Related Matters with members of Atkore’s legal team and outside counsel. Seven potential bidders, including Prysmian, Bidder B, Bidder C and Bidder E (as defined below) and other potential strategic and financial sponsor bidders, were provided with access to Atkore’s updated confidential information presentation, quality of earnings materials and a limited virtual data room containing selected diligence materials.

During this time, one potential bidder indicated that it would not participate further in the process while the Antitrust Investigation remained outstanding, while Bidder E expressed continued interest and requested an opportunity to meet with Atkore management.

On May 10, 2026, Bidder C made a verbal proposal to acquire Atkore for $85.00 per share, consisting of $25.00 in cash and $60.00 in Bidder C’s common stock, qualified by reference to the Antitrust and Related Matters.

Between May 19, 2026 and May 23, 2026, representatives of Citi and J.P. Morgan sent additional diligence materials reflecting developments in Atkore’s business and the Antitrust and Related Matters, as well as a clean team agreement, to seven potential bidders, including Prysmian, Bidder A, Bidder B, Bidder C, Bidder D and Bidder E.

Also on May 19, 2026, members of Prysmian’s executive team toured Atkore’s Hobart, Indiana and Harvey, Illinois facilities. On the same date, Atkore held a general management diligence session and a legal diligence session with members of Prysmian’s executive team.

On May 29, 2026, Citi and J.P. Morgan, on behalf of Atkore, sent an updated process letter to participants in the Atkore sale process, requesting non-binding indications of interest from bidders by June 17, 2026.

On June 3, 2026, Atkore entered into an agreement, subject to court approval, to settle with the third and final class of plaintiffs in the In re PVC Pipe Antitrust Litigation putative class action lawsuit against Atkore, for the payment of an aggregate of $50 million into a settlement fund.

On June 4, 2026, Atkore management held a diligence call with representatives of Bidder C.

Throughout June 2026, six potential bidders conducted diligence on Atkore, including site visits and meetings with the Atkore management team. On June 16, 2026, certain potential bidders, including Bidder B, notified Atkore and its advisors that they would not be submitting bids, citing, among other reasons, risks relating to the remaining Antitrust and Related Matters.

On June 17, 2026, Atkore and its advisors received four non-binding indications of interest (the “June Bids”):

Additionally, as part of the process that resulted in the June Bids, Atkore and its advisors also received verbal indications from certain other potential bidders who noted that they would only be interested in acquiring a portion of Atkore’s business.

On June 19, 2026, the Strategic Review Committee met by means of remote communication, along with representatives of Citi, J.P. Morgan and Debevoise, to discuss and compare the June Bids and the status of the Atkore sale process, including parties who declined to submit bids and reasons therefor. In connection with the Strategic Review Committee’s discussion of the June Bids, representatives of Citi presented the financial terms of the June Bids, including the premiums implied by the June Bids. The Strategic Review Committee then discussed next steps in the process, including the scheduling of a meeting of the full Board to review the current status and make any decisions regarding next steps with each of the bidders.

On June 23, 2026, the Board held a meeting via means of remote communication, which included senior management of Atkore and representatives of Debevoise, Citi and J.P. Morgan. During the meeting, Debevoise presented to the Board on fiduciary duties applicable to directors under Delaware law, including the applicable legal standards in connection with the sale process. The Board discussed such applicable duties and asked Debevoise questions regarding such duties under certain circumstances. Later in the meeting, Citi and J.P. Morgan presented to the Board on the status of the Atkore sale process, including (i) a summary and comparison of the June Bids, (ii) the premiums implied by the June Bids and (iii) a summary of which parties declined to submit bids and the reasons therefor. The Board determined that Atkore should prioritize a sale of the whole company rather than certain parts thereof. The Board, together with Citi, J.P. Morgan and Debevoise, then discussed next steps in the Atkore sale process.

On June 23, 2026, bidders, including Prysmian, Bidder C and Bidder E received access to the “Round 2” virtual data room.

Throughout the end of June and the beginning of July 2026, Prysmian, Bidder C and Bidder E conducted diligence, including meetings between representatives of each of Prysmian, Bidder C and Bidder E and advisors and/or management of Atkore, covering the following topics, among others: accounting; quality of earnings; procurement; management presentations; legal; antitrust; litigation; financial modeling; environmental; and go-to-market. The legal diligence included updates on the Antitrust Litigation, the Antitrust Investigation and the Stockholder Litigation.

On July 7, 2026, two versions of the auction draft of the Merger Agreement were made available to bidders, one that was distributed to all-cash bidders (including Prysmian and Bidder E) and one that was delivered to cash/stock-mix bidders (including Bidder C).

On July 10, 2026, representatives of Citi and J.P. Morgan, on behalf of Atkore, sent a process letter to Prysmian, Bidder C and Bidder E, requesting final bids, including final-form transaction documents, from each bidder by August 6, 2026. Initial markups of the Merger Agreement were requested to be delivered to Debevoise by July 24, 2026 to allow time to discuss transaction documents prior to the final bid date.

Throughout the second half of July 2026, Prysmian, Bidder C and Bidder E continued to conduct confirmatory due diligence on Atkore, including management meetings, site visits and financial, operational, legal, litigation, tax and other diligence sessions. In connection with Bidder C’s proposal to provide a portion of the consideration in Bidder C common stock, Atkore also conducted reverse diligence on Bidder C, including management presentations and site visits.

On July 16, 2026, the Board and the Strategic Review Committee held a joint meeting via means of remote communication, which included representatives of Debevoise, Citi and J.P. Morgan. During the meeting, the Board and the Strategic Review Committee discussed, together with Debevoise, the directors’ fiduciary duties in connection with a proposed transaction. Representatives of Citi and J.P. Morgan updated the Board and the Strategic Review Committee regarding the status of the Atkore sale process, including that Prysmian, Bidder C and Bidder E remained active in the process and were conducting due diligence, that Atkore was conducting reverse diligence on Bidder C and the anticipated timeline to final bids and execution of definitive transaction documents. Citi and J.P. Morgan also each presented their respective preliminary financial analyses to the Board and the Strategic Review Committee based on financial information and projections prepared by Atkore management. The financial advisors noted that additional work remained to be completed before they could finalize their respective financial analyses and render any potential fairness opinions. The Board and the Strategic Review Committee discussed and asked questions regarding the preliminary financial analyses with representatives of Citi and J.P. Morgan.

On July 23, 2026, initial drafts of the Company Disclosure Letter were made available to bidders.

On July 24, 2026, outside counsel for each of Prysmian and Bidder C, respectively, submitted a markup of the draft merger agreement for the proposed transaction. Also on July 24, 2026, Debevoise had a meeting by means of remote communication with Prysmian’s outside counsel, Wachtell, Lipton, Rosen & Katz (“Wachtell Lipton”), to discuss regulatory matters in connection with the proposed transaction, including Prysmian’s obligations to obtain required regulatory approvals.

On July 28, 2026, a representative from the financial advisor to Bidder C informed a representative of Citi that Bidder C’s revised bid would include a contingent value right (“CVR”) to account for certain of the Antitrust and Related Matters (the “Covered Litigation”). Later that day, Bidder C’s outside counsel sent a CVR term sheet to Debevoise.

On July 28, 2026, Debevoise met with each of Wachtell Lipton and Bidder C’s outside counsel to provide feedback on the bidders’ markups to the merger agreement. Key issues discussed with Wachtell Lipton included regulatory efforts and closing conditions and certain interim operating covenants. Key issues discussed with Bidder C’s outside counsel included financing cooperation, post-closing governance and certain interim operating covenants. Additionally, Bidder C’s counsel reiterated that Bidder C’s bid would include a CVR accounting for the Covered Litigation as part of the mix of consideration.

On July 29, 2026, the Board and the Strategic Review Committee held a combined meeting, which included senior management of Atkore and representatives from Debevoise, Citi and J.P. Morgan. During the meeting, Debevoise presented to the Board and the Strategic Review Committee on the status of the contract negotiations with Prysmian and Bidder C. In particular, Debevoise noted the potential regulatory implications of a transaction with Prysmian. Debevoise then discussed the CVR proposed as part of Bidder C’s bid, including that (i) the CVR portion of the consideration would represent deferred consideration that would not become payable, if at all, until the Covered Litigation is finally resolved, (ii) any such amounts payable would be reduced by a portion of the liabilities incurred in connection with the Covered Litigation, with any amount ultimately paid to former Atkore stockholders depending on the results of such final resolution, with former Atkore stockholders bearing the cost of 100% of a “retention amount” and a portion of the liabilities above that amount, (iii) Bidder C would have full control over the Covered Litigation, and (iv) the CVR would be non-transferable. Thereafter, representatives from Citi updated the Board and the Strategic Review Committee regarding the status of the bidders’ due diligence. Citi reported to the Board and the Strategic Review Committee that Prysmian had indicated that it might seek to accelerate its bid. The Board and the Strategic Review Committee then discussed this possibility with Citi and J.P. Morgan. Finally, the Board and the Strategic Review Committee discussed the characteristics of each potential transaction, including the synergies with each bidder, regulatory implications and the uncertainty of the actual value and timing of payment of the CVR proposed by Bidder C.

On July 30, 2026, Prysmian submitted to the Board, via Citi, a revised proposal (the “July 30 Proposal”), which noted that Prysmian’s critical diligence was complete and the transaction was approved by Prysmian’s board, and included an increased price of $93.00 per share in cash, which accounted for potential liabilities arising from the Antitrust and Related Matters. Other terms in Prysmian’s July 30 Proposal included: (i) that Prysmian would be the purchasing entity under the merger agreement, and that Prysmian was prepared to offer a guarantee of Prysmian’s obligations by its principal U.S. subsidiary, (ii) that the transaction would be financed with cash on hand and third party financing, and the transaction would not be conditioned on financing and (iii) that appropriate employee

retention and incentive arrangements would be expected to be implemented for key employees to support a successful transition. Citi reported that Prysmian was working toward being able to announce an agreed transaction by August 3. Also on July 30, 2026, Wachtell Lipton sent Debevoise an incrementally revised markup of the merger agreement along with a markup of the Company Disclosure Letter, and, later, drafts of the exhibits to the merger agreement and an initial draft Buyer Disclosure Letter (as defined in the Merger Agreement). Later on July 30, 2026, Debevoise sent a revised draft of the merger agreement back to Wachtell Lipton.

Later on July 30, 2026, the Board and the Strategic Review Committee held a combined meeting, which included senior management of Atkore and representatives from Debevoise, Citi and J.P. Morgan. During the meeting, the Board discussed Prysmian’s July 30 Proposal. The Board approved the negotiation of definitive documents with Prysmian with the goal of coming to an agreement prior to Atkore’s third quarter earnings call. The Board also directed Citi to seek a higher price from Prysmian. Thereafter, representatives of Citi called representatives of Prysmian to relay Atkore’s feedback to the July 30 Proposal with a request to submit their best proposal on value.

On July 31, 2026, Prysmian submitted to the Board, via representatives of Citi and J.P. Morgan, a second revised proposal (the “July 31 Proposal”), in which Prysmian further increased its price to $95.00 per share in cash and confirmed that it was working towards finalizing definitive documentation and announcing the transaction on the morning of August 3, 2026, prior to Atkore’s earnings announcement. On the same day, Wachtell Lipton sent a revised draft of the merger agreement back to Debevoise.

Additionally, at the Board’s direction, on July 31, 2026, representatives of Citi contacted representatives of Bidder C’s financial advisors to clarify Bidder C’s proposed CVR mechanism. Bidder C’s advisors confirmed that the CVR would not constitute additional consideration on top of Bidder C’s previously communicated proposal but rather make up a portion of the aggregate consideration (in addition to cash and stock) in the revised proposal to be submitted by Bidder C. The representatives of Citi relayed this information to the Board and senior management.

Throughout August 1, 2026 and August 2, 2026, Debevoise and Wachtell Lipton traded drafts of the Company Disclosure Letter, the Buyer Disclosure Letter and the merger agreement and representatives of Debevoise and Wachtell Lipton held meetings to discuss comments on the merger agreement and the Company Disclosure Letter.

At mid-day on August 2, 2026, representatives of Bidder C called representatives of Citi and delivered a revised oral offer at a price of $87.00 per share, with $25.00 in cash and $62.00 in Bidder C’s stock. At this time, Bidder C’s proposal no longer included a CVR. Later, during the evening on August 2, 2026, representatives of Bidder C called representatives of Citi and delivered a second revised oral offer at a price of $87.00 per share, with $25.00 in cash and $62.00 in Bidder C’s stock, plus an additional $10.00 per share in the form of a CVR without specifying the terms of the CVR.

On August 2, 2026, the Board held a meeting via means of remote communication which included senior management of Atkore and representatives from Debevoise, Citi and J.P. Morgan. During the meeting, Debevoise reviewed with the Board the directors’ fiduciary duties in connection with the proposed transaction. Debevoise also reviewed with the Board the terms of the Merger Agreement, which had been fully negotiated between Atkore and Prysmian and their respective counsel. Citi and J.P. Morgan reviewed with the Board and compared the financial terms of the latest all-cash offer by Prysmian and the latest part-cash, part-stock and CVR offer by Bidder C, including a review of the CVR being offered by Bidder C. The Board then discussed the relative strength of the proposals by Prysmian and Bidder C and unanimously determined that Prysmian’s July 31 Proposal was more compelling. Thereafter, Citi and J.P. Morgan each reviewed with the Board their respective financial analyses of the Merger Consideration. Representatives of Citi then rendered to the Board Citi’s oral opinion, subsequently confirmed by the delivery of a written opinion, dated August 2, 2026, to the effect that, as of that date and based on and subject to various assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken by Citi as set forth in its written opinion, the Merger Consideration to be received by the holders of Common Stock in the Merger pursuant to the Merger Agreement was fair, from a financial point of view, to such holders. Thereafter, representatives of J.P. Morgan rendered to the Board J.P. Morgan’s oral opinion, subsequently confirmed by the delivery of a written opinion, dated August 3, 2026, to the effect that, as of that date and based on and subject to various assumptions made, procedures followed, matters considered and limitations and

qualifications on the review undertaken by J.P. Morgan as set forth in its written opinion, the Merger Consideration to be received by the holders of Common Stock pursuant to the Merger Agreement in the proposed transaction was fair, from a financial point of view, to such holders. For more information, see the section entitled “—Opinions of Atkore’s Financial Advisors.”

Following discussion among the Board, the Board unanimously (i) determined that the terms of the Merger Agreement and the transactions contemplated thereby, including the Merger, are fair to, and in the best interests of, Atkore and its stockholders; (ii) determined that it is in the best interests of Atkore and its stockholders and declared it advisable to enter into the Merger Agreement; (iii) approved the execution and delivery by Atkore of the Merger Agreement, the performance by Atkore of its covenants and agreements contained therein and the consummation of the transactions contemplated by the Merger Agreement, including the Merger, upon the terms and subject to the conditions set forth therein; (iv) resolved to recommend that the stockholders of Atkore approve the Merger and adopt the Merger Agreement; and (v) directed that the Merger Agreement be submitted to the stockholders of Atkore for its adoption.

Promptly following the meeting of the Board on August 2, 2026, Atkore and Prysmian exchanged signature pages to the Merger Agreement, and the Merger Agreement became effective.

The Board has unanimously (i) determined that the terms of the Merger Agreement and the transactions contemplated thereby, including the Merger, are fair to, and in the best interests of, Atkore and its stockholders; (ii) determined that it is in the best interests of Atkore and its stockholders and declared it advisable to enter into the Merger Agreement; (iii) approved the execution and delivery by Atkore of the Merger Agreement, the performance by Atkore of its covenants and agreements contained therein and the consummation of the transactions contemplated by the Merger Agreement, including the Merger, upon the terms and subject to the conditions set forth therein; (iv) resolved to recommend that the stockholders of Atkore approve the Merger and adopt the Merger Agreement; and (v) directed that the Merger Agreement be submitted to the stockholders of Atkore for its adoption.

The Board unanimously recommends that the holders of shares of Common Stock vote “FOR” the Merger Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

In evaluating the Merger, the Board consulted with Atkore’s management team and legal and financial advisors and considered the following potentially positive factors, which are not intended to be exhaustive and are not presented in any relative order of importance:

The Board also considered and balanced the factors described above against potentially negative factors and risks associated with the Merger, including the following factors, which are not intended to be exhaustive and are not presented in any relative order of importance:

The Board considered the factors described above as a whole, including by engaging in discussions with members of Atkore’s management team and legal and financial advisors. Based on this review and consideration, the Board unanimously concluded that these factors, on balance, supported a determination that the potentially negative factors relevant to the Merger were outweighed by the potential benefits of the Merger and that the Merger was more favorable to Atkore and its stockholders than the other alternatives reasonably available to Atkore.

The foregoing discussion of the factors considered by the Board is not intended to be exhaustive but, rather, summarizes the material information and factors considered by the Board in its consideration of the Merger. In view of the wide variety of factors considered by the Board in connection with its evaluation of the Merger and the complexity of these matters, the Board did not quantify or assign relative weights to the factors considered, and individual members of the Board may have given different weights to different factors. The Board based its unanimous recommendation on the totality of the information presented.

The foregoing discussion of the information and factors considered by the Board is forward-looking in nature and should be read in light of the factors described in the section titled “Cautionary Statement Regarding Forward-Looking Statements.”

Atkore retained Citi as its financial advisor in connection with a possible transaction involving Prysmian. In connection with Citi’s engagement, Atkore requested that Citi evaluate the fairness, from a financial point of view, to the holders of Common Stock of the Merger Consideration pursuant to the Merger Agreement. On August 2, 2026, at a meeting of the Board held to evaluate the Merger and at which the Merger Agreement was approved, Citi rendered to the Board an oral opinion, confirmed by delivery of a written opinion, dated August 2, 2026, to the effect that, as of that date and based on and subject to various assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken by Citi as set forth in its written opinion, the Merger Consideration to be received by the holders of Common Stock in the Merger pursuant to the Merger Agreement was fair, from a financial point of view, to such holders.

The full text of Citi’s written opinion, dated August 2, 2026, to the Board, which sets forth, among other things, the assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken by Citi in rendering its opinion, is attached to this proxy statement as Annex B and is incorporated herein by reference in its entirety. The summary of Citi’s opinion set forth below is qualified in its entirety by reference to the full text of Citi’s opinion. Citi’s opinion was rendered to the Board (in its capacity as such) in connection with its evaluation of the Merger and was limited to the fairness, from a financial point of view, to the holders of Common Stock of the Merger Consideration pursuant to the Merger Agreement. Citi’s opinion did not address any other terms, aspects or implications of the Merger. Citi’s opinion is not intended to be and does not constitute a recommendation to any stockholder as to how such stockholder should vote or act on any matters relating to the Merger.

In arriving at its opinion, Citi:

In addition to the foregoing, Citi conducted such other analyses and examinations and considered such other information and financial, economic and market criteria as Citi deemed appropriate in arriving at its opinion. The issuance of Citi’s opinion was authorized by Citi’s fairness opinion committee.

In rendering its opinion, Citi assumed and relied, without independent verification, upon the accuracy and completeness of all financial and other information and data publicly available or provided to or otherwise reviewed by or discussed with Citi and upon the assurances of the management of Atkore that they were not aware of any relevant information that had been omitted or that remained undisclosed to Citi. With respect to financial forecasts and other information and data relating to Atkore provided to or otherwise reviewed by or discussed with Citi, Citi was advised by the management of Atkore, and Citi assumed, with the Board’s consent, that such forecasts and other information and data were reasonably prepared in good faith on bases reflecting the best currently available estimates and judgments of the management of Atkore as to, and were a reasonable basis upon which to evaluate, the future financial performance of Atkore. Citi expressed no view or opinion as to any financial and other information or data (or any underlying assumptions on which any such financial and other information or data are based) provided to or otherwise reviewed by or discussed with Citi.

Citi assumed, with the Board’s consent, that the Merger would be consummated in accordance with the terms, conditions and agreements set forth in the Merger Agreement, and in compliance with all applicable laws, documents and other requirements, without waiver, modification or amendment of any material term, condition or agreement and that, in the course of obtaining the necessary governmental, regulatory or third party approvals, consents and releases for the Merger, no delay, limitation, restriction or condition would be imposed or occur that would have an adverse effect on Atkore or the Merger (including the contemplated benefits thereof) or that otherwise would be meaningful in any respect to Citi’s analyses or opinion. Representatives of Atkore advised Citi, and Citi further assumed, that the final terms of the Merger Agreement would not vary, in any material respect, from those set forth in the draft reviewed by Citi. Citi did not make, and was not provided with, an independent evaluation or appraisal of the assets or liabilities (contingent, derivative, off-balance sheet, accrued or otherwise) of Atkore or any other business or person, nor did Citi make any physical inspection of the properties or assets of Atkore or any other business or person. Citi’s opinion did not address any terms (other than the Merger Consideration to the extent expressly specified in Citi’s opinion), aspects or implications of the Merger, including, without limitation, the form or structure of the Merger, or any other agreement, arrangement or understanding to be entered into in connection with, related to or contemplated by the Merger or otherwise. Citi did not express any opinion as to the prices at which the Common Stock would trade at any time, or any other securities would trade or otherwise be transferable at any time, including following the announcement of the Merger. Citi did not evaluate the solvency or fair value of Atkore, or any other entity under any state, federal or other laws relating to bankruptcy, insolvency or similar matters. Citi expressed no view as to, and its opinion did not address, the underlying business decision of Atkore to effect or enter into the Merger, the relative merits of the Merger as compared to any alternative business strategies that might exist for Atkore or the effect of any other transaction in which Atkore might engage or that Atkore might consider. Citi also expressed no view as to, and its opinion did not address, the fairness (financial or otherwise) of the amount or nature or any other aspect of any compensation or other consideration to any officers, directors or employees of any parties to the Merger (in their capacity as such), or any class of such persons, relative to the Merger Consideration or otherwise. Citi did not express any opinion or view with respect to accounting, tax, regulatory, legal or similar matters and Citi relied, with the Board’s consent, upon the assessments of representatives of Atkore as to such matters. Citi’s opinion was necessarily based upon information available to Citi, and financial, stock market and other conditions and circumstances existing, as of the date of its opinion. Although subsequent developments might affect Citi’s opinion, Citi has no obligation to update, revise or reaffirm its opinion.

In preparing its opinion, Citi performed a variety of financial and comparative analyses, including those described below. The preparation of a financial opinion is a complex analytical process involving various determinations as to the most appropriate and relevant methods of financial analysis and the application of those methods to the particular circumstances and, therefore, a financial opinion is not readily susceptible to partial analysis or summary description. Citi arrived at its opinion based on the results of all analyses undertaken by it and factors assessed as a whole, and it did not draw, in isolation, conclusions from or with regard to any one factor or method of analysis for purposes of its opinion.

The estimates used by Citi for purposes of its analyses and the valuation ranges resulting from any particular analysis are not necessarily indicative of actual values or predictive of future results or values, which may be significantly more or less favorable than those suggested by such analyses. In addition, analyses relating to the value of businesses or securities do not purport to be appraisals or to reflect the prices at which businesses or securities actually may be sold or acquired. Accordingly, the estimates used in, and the results derived from, Citi’s analyses are inherently subject to substantial uncertainty.

Citi was not requested to, and it did not, recommend or determine the specific consideration payable in the Merger. The type and amount of consideration payable in the Merger were determined through negotiations between Atkore and Prysmian and Atkore’s decision to enter into the Merger Agreement was solely that of the Board. Citi’s opinion was only one of many factors considered by the Board in its evaluation of the Merger and should not be viewed as determinative of the views of the Board or the management of Atkore with respect to the Merger, the Merger Consideration or any other aspect of the transactions contemplated by the Merger Agreement.

The following is a summary of the material financial analyses prepared for and reviewed with the Board in connection with the rendering of Citi’s opinion, dated August 2, 2026, to the Board. The summary set forth below does not purport to be a complete description of the financial analyses performed by, and underlying the opinion of, Citi, nor does the order of the financial analyses described represent the relative importance or

weight given to those financial analyses by Citi. Certain financial analyses summarized below include information presented in tabular format. In order to fully understand the financial analyses, the tables must be read together with the text of each summary as the tables alone do not constitute a complete description of the financial analyses. Considering the data in the tables below without considering the full narrative description of the financial analyses, including the methodologies and assumptions underlying the financial analyses, could create a misleading or incomplete view of such financial analyses. Future results may be different from those described and such differences may be material. Approximate implied equity value per share reference ranges derived from the financial analyses described below and other per share ranges presented for reference purposes only were rounded to the nearest $0.05, except with respect to the 52-week trading range analysis. Financial data utilized for Atkore in the financial analyses described below, to the extent based on financial forecasts and estimates of management, were based on certain financial forecasts and other information and data relating to Atkore provided to or discussed with Citi by the management of Atkore, and approved for Citi’s use by the Board (see the “Prospective Financial Information,” as further summarized in the section titled “—Certain Unaudited Prospective Financial Information”).

Citi conducted a discounted cash flow analysis of Atkore using the Prospective Financial Information (as defined below) for the purpose of determining an implied fully diluted equity value per share for the Common Stock. Citi calculated the estimated present value of unlevered free cash flows that Atkore was forecasted to generate during the period from the fourth quarter of fiscal year ending September 30, 2026 through fiscal year ending September 30, 2030 based on the Prospective Financial Information. Citi calculated a range of illustrative terminal values for Atkore as of September 30, 2030 by applying a selected range of perpetuity growth rates of 1.5% to 2.5% to an estimate of Atkore’s unlevered free cash flow in the terminal year based on the Prospective Financial Information. The unlevered free cash flows and the range of terminal values were then discounted to present values, as of June 30, 2026, using mid-year discounting convention and discount rates ranging from 11.3% to 12.9%, to derive ranges of implied enterprise value for Atkore. Citi adjusted the range of implied enterprise values it derived for Atkore for Atkore’s net debt, payments related to a litigation settlement made after the quarter ended June 26, 2026, and a payment related to Atkore’s HDPE divestiture after the quarter ended June 26, 2026, in each case, as of June 30, 2026, as provided by Atkore’s management, added a range of present values of Atkore’s tax benefits from Federal net operating losses carry forwards, and divided the results by the diluted Common Stock share count of Atkore calculated using the treasury stock method, based on equity information as of July 31, 2026 as provided by Atkore’s management. The range of present values of Atkore’s tax benefits from Federal net operating losses carry forwards was calculated by discounting to present values, as of June 30, 2026, estimates of Atkore’s tax benefits from Federal net operating losses carry forwards, as provided in the Prospective Financial Information, using mid-year discounting convention and a discount rate of 5.4%. This analysis indicated an approximate implied per share equity value reference range for Atkore of $74.90 to $98.05 without the tax attributes, and $76.65 to $99.80 taking the tax attributes into account, as compared to the closing share price of the Common Stock as of July 31, 2026, of $72.96, and the Merger Consideration of $95.00.

Citi reviewed certain publicly available financial and stock market information of Atkore and the selected companies listed in the table below, which are collectively referred to as the “selected companies”:

Although none of the selected companies is directly comparable to Atkore, the companies included were chosen because they have operations that, for purposes of Citi’s analysis and based on its experience and professional judgment, may be considered generally relevant in evaluating those of Atkore based on business sector participation, operational characteristics and financial metrics. The quantitative information used in this analysis, to the extent that it is based on market data, was based on market data as of July 31, 2026.

For each of the selected companies, and for Atkore for reference, Citi calculated and reviewed, among other information, enterprise value as a multiple of 2026 calendar year estimated earnings before interest, taxes, depreciation and amortization (“EBITDA”) (such multiple, “EV / 2026E EBITDA”). Financial data of the selected companies were based on Wall Street research analysts’ estimates and other publicly available information. With respect to the multiples calculated for Atkore for reference, the financial data of Atkore was based on Wall Street research analysts’ estimates, other publicly available information and information provided by Atkore’s management.

Based on its professional judgment and experience, and taking into consideration the observed multiples for the selected companies, Citi then applied an illustrative EV / 2026E EBITDA multiple reference range of 6.9x to 10.3x to an estimate of Atkore’s 2026 calendar year Adjusted EBITDA based on the Prospective Financial Information, to derive ranges of implied enterprise value for Atkore. Citi adjusted the range of implied enterprise values it derived for Atkore, for Atkore’s net debt, payments related to a litigation settlement made after the quarter ended June 26, 2026, and a payment related to Atkore’s HDPE divestiture, in each case, as of June 30, 2026, as provided by Atkore’s management, and divided the results by the diluted Common Stock share count of Atkore calculated using the treasury stock method, based on equity information as of July 31, 2026 as provided by Atkore’s management. This analysis indicated an approximate implied per share equity value reference range for Atkore of $65.70 to $104.35, as compared to the closing share price of the Common Stock as of July 31, 2026, of $72.96, and the Merger Consideration of $95.00.

Using publicly available information, Citi performed a selected precedent transactions analysis of Atkore in which Citi reviewed financial data relating to the four selected transactions listed in the table below that Citi considered generally relevant for purposes of analysis, which are collectively referred to as the “selected transactions”:

Although none of the target companies in the selected transactions are directly comparable to Atkore and none of the selected transactions are directly comparable to the transactions contemplated by the Merger Agreement, the selected transactions were chosen because they involved businesses with financial, operational or business characteristics that, in Citi’s view, based on its professional judgment and experience, made them sufficiently comparable to Atkore and/or the transaction contemplated by the Merger Agreement or otherwise relevant for purposes of analysis.

For each of the selected transactions, Citi reviewed, among other information, the ratio of the target company’s firm value (calculated as the publicly disclosed transaction value) to the target company’s EBITDA for the specified prior 12 month period disclosed at the time the transaction was announced (“FV / EBITDA”). Financial data of the selected transactions were based on public filings and other publicly available information.

Based on its professional judgment and experience and taking into consideration the observed multiples for the selected transactions, Citi then applied an illustrative FV / EBITDA multiple reference range of 8.2x to 10.0x to the fiscal year 2026 EBITDA of Atkore, to derive ranges of implied firm value for Atkore. Citi adjusted the range of implied firm values it derived for Atkore for Atkore’s net debt, payments related to a litigation settlement made after

the quarter ended June 26, 2026, and a payment related to Atkore’s HDPE divestiture after the quarter ended June 26, 2026, in each case, as of June 30, 2026, as provided by Atkore’s management, and divided the results by the diluted Common Stock share count of Atkore calculated using the treasury stock method, based on equity information as of July 31, 2026 as provided by Atkore’s management. This analysis indicated an approximate implied per share equity value reference range for Atkore of $74.55 to $93.45, as compared to the closing share price of the Common Stock as of July 31, 2026, of $72.96, and the Merger Consideration of $95.00.

Citi observed certain other information with respect to Atkore that was not considered part of its financial analyses with respect to its opinion, but was noted for reference purposes only, including the following:

Citi reviewed the historical closing share prices of the Common Stock for the 52-week period ended July 31, 2026. Citi noted that the low and high closing prices of the Common Stock during this period were approximately $53.49 and $90.16 per share, as compared to the closing share price of the Common Stock as of July 31, 2026, of $72.96, and the Merger Consideration of $95.00.

Citi reviewed the most recent publicly available research analysts’ one-year forward price targets for the Common Stock prepared and published by selected research analysts. Citi noted that as of July 31, 2026, such price targets ranged from $76.00 to $86.00 per share for the Common Stock. Citi also noted that these ranges of price targets, discounted one year at an estimated 13.5%, reflecting a mid-point estimate of Atkore’s cost of equity, was $67.35 to $78.10 per share for the Common Stock, as compared to the closing share price of the Common Stock as of July 31, 2026, of $72.96, and the Merger Consideration of $95.00.

Atkore has agreed to pay Citi for its services in connection with the Merger an aggregate fee estimated based on information available as of the date of this proxy statement to be up to approximately $38 million, of which $2.5 million was payable in connection with the delivery of Citi’s opinion to the Board and up to $1.75 million is payable at Atkore’s sole discretion based on Atkore’s assessment of Citi’s performance of its services. In addition, Atkore agreed to reimburse Citi for certain expenses and to indemnify Citi against certain liabilities arising from Citi’s engagement.

As the Board was aware, Citi and its affiliates in the past have provided, currently are providing and in the future may provide, certain investment banking, commercial banking and other similar services to Atkore and/or its affiliates unrelated to the Merger, for which services Citi and such affiliates have received and expect to receive compensation, including, without limitation, during the two-year period prior to the date of Citi’s opinion, having acted as financial advisor with respect to certain merger and acquisition matters and as co-documentation agent, bookrunner and lender with respect to certain credit facilities and loans of Atkore and having provided or providing certain markets and securities services and treasury and trade solutions services. For the services described above for Atkore, Citi and its affiliates received, during the two-year period prior to the date of Citi’s opinion, aggregate fees of approximately $4 million from Atkore and/or certain of its affiliates. In addition, as the Board was further aware, Citi and its affiliates in the past have provided, currently are providing and in the future may provide investment banking, commercial banking and other similar financial services to Prysmian and/or its affiliates unrelated to the Merger, for which services Citi and such affiliates have received and expect to receive compensation, including, without limitation, during the two-year period prior to the date of Citi’s opinion, having acted or acting as underwriter, master lead arranger and lender with respect to certain credit facilities, loans and bond issuances of Prysmian, and having provided or providing certain markets and securities services and treasury and trade solutions services. For the services described above for Prysmian, Citi and its affiliates received, during the two-year period prior to the date of Citi’s opinion, aggregate fees of approximately $8 million from Prysmian and/or certain of its affiliates. In the ordinary course of its business, Citi and its affiliates may actively trade or hold the securities or financial instruments (including loans and other obligations) of Atkore, Prysmian, and their respective affiliates for Citi’s own account or for the account of Citi’s customers and, accordingly, may at any time hold a long or short position or otherwise effect transactions in such securities or financial instruments. In addition, Citi and its affiliates (including Citigroup Inc. and its affiliates) may maintain relationships with Atkore, Prysmian, and their respective affiliates. As of July 31, 2026, Citi held, on a proprietary basis, less than 1.0% of the outstanding equity securities of (i) Atkore and (ii) Prysmian, respectively.

Atkore selected Citi to act as its financial advisor in connection with the Merger based on Citi’s reputation, experience and familiarity with Atkore and its business. Citi is an internationally recognized investment banking firm that regularly engages in the valuation of businesses and their securities in connection with mergers and acquisitions, negotiated underwritings, competitive bids, secondary distributions of listed and unlisted securities, private placements and valuations for estate, corporate and other purposes.

Atkore retained J.P. Morgan as its financial advisor in connection with a possible transaction involving Prysmian. In connection with J.P. Morgan’s engagement, Atkore requested that J.P. Morgan evaluate the fairness, from a financial point of view, to the holders of Common Stock of the Merger Consideration pursuant to the Merger Agreement. On August 2, 2026, at a meeting of the Board held to evaluate the Merger and at which the Merger Agreement was approved, J.P. Morgan rendered its oral opinion to the Board that, as of such date, and based upon and subject to the assumptions made, procedures followed, matters considered and limitations on the review undertaken by J.P. Morgan in preparing its opinion, the Merger Consideration to be paid to the holders of Common Stock in the Merger was fair, from a financial point of view, to such holders. J.P. Morgan confirmed its August 2, 2026 oral opinion by delivering its written opinion, dated as of August 3, 2026, to the Board that, as of the date of such opinion, the consideration to be paid to the holders of Common Stock in the Merger was fair, from a financial point of view, to such holders.

The full text of the written opinion of J.P. Morgan, dated August 3, 2026, which sets forth, among other things, the assumptions made, procedures followed, matters considered and limitations on the review undertaken by J.P. Morgan in preparing its opinion, is attached as Annex C to this proxy statement and is incorporated herein by reference. The summary of the opinion of J.P. Morgan set forth in this proxy statement is qualified in its entirety by reference to the full text of such opinion. Atkore’s stockholders are urged to read the opinion in its entirety. J.P. Morgan’s opinion was addressed to the Board (in its capacity as such) in connection with and for the purposes of its evaluation of the Merger, was directed only to the consideration to be paid to the holders of Common Stock in the Merger and did not address any other aspect of the Merger. J.P. Morgan expressed no opinion as to the fairness of the consideration to be paid in connection with the Merger to the holders of any other class of securities, creditors or other constituencies of Atkore or as to the underlying decision by Atkore to engage in the Merger. The issuance of J.P. Morgan’s opinion was approved by a fairness committee of J.P. Morgan. The opinion does not constitute a recommendation to any stockholder of Atkore as to how such stockholder should vote with respect to the Merger or any other matter.

In arriving at its opinion, J.P. Morgan, among other things:

In addition, J.P. Morgan held discussions with certain members of the management of Atkore with respect to certain aspects of the Merger, the past and current business operations of Atkore, the financial condition and future prospects and operations of Atkore, and certain other matters J.P. Morgan believed necessary or appropriate to its inquiry.

In giving its opinion, J.P. Morgan relied upon and assumed the accuracy and completeness of all information that was publicly available or was furnished to or discussed with J.P. Morgan by Atkore or otherwise reviewed by or

for J.P. Morgan. J.P. Morgan did not independently verify any such information or its accuracy or completeness, and, pursuant to J.P. Morgan’s engagement letter with Atkore, J.P. Morgan did not assume any obligation to undertake any such independent verification. J.P. Morgan did not conduct and was not provided with any valuation or appraisal of any assets or liabilities, nor did J.P. Morgan evaluate the solvency of Atkore or Prysmian under any state and federal laws relating to bankruptcy, insolvency or similar matters. In relying on financial analyses and forecasts provided to J.P. Morgan or derived therefrom, J.P. Morgan assumed that they were reasonably prepared based on assumptions reflecting the best currently available estimates and judgments by Atkore’s management as to the expected future results of operations and financial condition of Atkore to which such analyses or forecasts relate. J.P. Morgan expressed no view as to such analyses or forecasts or the assumptions on which they were based. J.P. Morgan also assumed that the Merger and the other transactions contemplated by the Merger Agreement would be consummated as described in the Merger Agreement. J.P. Morgan also assumed that the representations and warranties made by Atkore and Prysmian in the Merger Agreement and the related agreements were and would be true and correct in all respects material to its analysis. J.P. Morgan is not a legal, regulatory or tax expert and relied on the assessments made by advisors to Atkore with respect to such issues. J.P. Morgan further assumed that all material governmental, regulatory or other consents and approvals necessary for the consummation of the Merger would be obtained without any adverse effect on Atkore or on the contemplated benefits of the Merger.

The projections furnished to J.P. Morgan were prepared by Atkore’s management as discussed more fully in the section titled “—Certain Unaudited Prospective Financial Information.” Atkore does not publicly disclose internal long-term management projections of the type provided to J.P. Morgan in connection with J.P. Morgan’s analysis of the Merger, and such projections were not prepared with a view toward public disclosure. These projections were based on numerous variables and assumptions that are inherently uncertain and may be beyond the control of Atkore’s management, including, without limitation, factors related to general economic and competitive conditions and prevailing interest rates. Accordingly, actual results could vary significantly from those set forth in such projections. For more information regarding the use of projections and other forward-looking statements, please refer to the section titled “—Certain Unaudited Prospective Financial Information.”

J.P. Morgan’s opinion was necessarily based on economic, market and other conditions as in effect on, and the information made available to J.P. Morgan as of, the date of such opinion. J.P. Morgan’s opinion noted that subsequent developments may affect J.P. Morgan’s opinion and that J.P. Morgan does not have any obligation to update, revise or reaffirm such opinion. J.P. Morgan’s opinion was limited to the fairness, from a financial point of view, of the Merger Consideration to be paid to the holders of Common Stock in the Merger, and J.P. Morgan expressed no opinion as to the fairness of any consideration to be paid in connection with the Merger to the holders of any other class of securities, creditors or other constituencies of Atkore or as to the underlying decision by Atkore to engage in the Merger. Furthermore, J.P. Morgan expressed no opinion with respect to the amount or nature of any compensation to any officers, directors or employees of any party to the Merger, or any class of such persons, relative to the Merger Consideration to be paid to the holders of Common Stock in the Merger or with respect to the fairness of any such compensation. The terms of the Merger Agreement, including the Merger Consideration, were determined through arm’s length negotiations between Atkore and Prysmian, and the decision to enter into the Merger Agreement was solely that of the Strategic Review Committee and the Board.

J.P. Morgan’s opinion and financial analyses were only one of the many factors considered by the Board in its evaluation of the Merger and should not be viewed as determinative of the views of the Strategic Review Committee, the Board or Atkore’s management with respect to the Merger or the consideration, including the Merger Consideration.

In accordance with customary investment banking practice, J.P. Morgan employed generally accepted valuation methodologies in rendering its opinion to the Board on August 2, 2026, which was confirmed by delivery of a written opinion, dated August 3, 2026, and in the financial analyses presented to the Board on such date in connection with the rendering of such opinion. The following is a summary of the material financial analyses utilized by J.P. Morgan in connection with rendering its opinion to the Board and does not purport to be a complete description of the analyses or data presented by J.P. Morgan. Some of the summaries of the financial analyses include information presented in tabular format. The tables are not intended to stand alone, and in order to more fully understand the financial analyses used by J.P. Morgan, the tables must be read together with the full text of each summary. Considering the data set forth below without considering the full narrative description of the financial analyses, including the methodologies and assumptions underlying the analyses, could create a misleading or incomplete view of J.P. Morgan’s analyses.

Using publicly available information, J.P. Morgan compared selected financial data of Atkore with similar data for selected publicly traded companies engaged in businesses that J.P. Morgan judged to be sufficiently analogous to Atkore’s business (or aspects thereof) based on J.P. Morgan’s experience and its familiarity with the industries in which Atkore operates. The companies selected by J.P. Morgan were as follows:

These companies were selected, among other reasons, because they are publicly traded companies with operations and businesses that, for purposes of J.P. Morgan’s analysis, may be considered to be similar to those of Atkore. However, certain of these companies may have characteristics that are materially different from those of Atkore. The analyses necessarily involve complex considerations and judgments concerning differences in financial and operational characteristics of the companies involved and other factors that could affect the selected companies differently than they would affect Atkore.

Using publicly available information, J.P. Morgan calculated, for each selected company, the multiple of the firm value (the “FV”) (calculated as equity value, plus or minus, as applicable, net debt or net cash) to the analyst consensus estimates of Adjusted EBITDA for the fiscal year 2026, with such EBITDA multiples calendarized to Atkore’s fiscal year ending September 30, 2026 (the “FV/2026E Adjusted EBITDA Multiple”). Based on the results of this analysis, J.P. Morgan selected a FV/2026E Adjusted EBITDA Multiple reference range for Atkore of 7.0x to 9.5x. J.P. Morgan then applied such reference range to Atkore’s projected fiscal year 2026 Adjusted EBITDA of $376 million, as set forth in the Prospective Financial Information. The analysis indicated a range of implied per share equity value for the Common Stock (rounded to the nearest $0.25) of approximately $61.75 to $88.50, which J.P. Morgan compared to (i) the closing share price of the Common Stock of $72.96 as of July 31, 2026, the trading day immediately preceding the date of J.P. Morgan’s written opinion and (ii) the Merger Consideration of $95.00.

Using publicly available information, J.P. Morgan examined selected transactions involving businesses which J.P. Morgan judged to be sufficiently analogous to Atkore’s business (or aspects thereof) based on J.P. Morgan’s experience and familiarity with the industries in which Atkore operates. The following transactions were selected by J.P. Morgan as relevant to the evaluation of the Merger:

None of the selected transactions reviewed was identical to the Merger. However, the selected transactions were chosen because certain aspects of the transactions, for purposes of J.P. Morgan’s analysis, may be considered similar to the Merger. The analyses necessarily involve complex considerations and judgments concerning differences in financial and operational characteristics of the companies involved and other factors that could affect the transactions differently than they would affect the Merger.

Using publicly available information, J.P. Morgan calculated, for each selected transaction, the multiple of the target company’s FV implied in the relevant transaction to the target company’s LTM Adjusted EBITDA for the twelve-month

period immediately preceding the announcement of the applicable transaction, or the closest available proxy depending on the availability of information (the “FV/LTM Adjusted EBITDA Multiple”). Based on the results of this analysis, J.P. Morgan selected a FV/LTM Adjusted EBITDA Multiple reference range for Atkore of 8.0x to 10.5x. J.P. Morgan then applied such reference range to Atkore’s Adjusted EBITDA of $352 million for the twelve months ended June 26, 2026. The analysis indicated a range of implied per share equity value for the Common Stock (rounded to the nearest $0.25) of approximately $67.00 to $92.25, which J.P. Morgan compared to (i) the closing share price of the Common Stock of $72.96 as of July 31, 2026 and (ii) the Merger Consideration of $95.00.

J.P. Morgan conducted a discounted cash flow analysis for the purpose of determining an implied fully diluted equity value per share for the Common Stock. J.P. Morgan calculated the unlevered free cash flows that Atkore is expected to generate from June 27, 2026 through fiscal year 2030 based upon the Prospective Financial Information, which were discussed with, and approved by, Atkore for use by J.P. Morgan in connection with its financial analyses. J.P. Morgan also calculated a range of terminal values for Atkore at the end of this period by applying perpetual growth rates ranging from 1.25% to 2.25%, based on guidance provided by Atkore’s management, to estimates of Adjusted EBITDA for Atkore at the end of fiscal year 2030, as provided in the Prospective Financial Information. J.P. Morgan then discounted the unlevered free cash flow estimates and the range of terminal values to present value as of June 26, 2026 using discount rates ranging from 9.5% to 11.5%, which range was chosen by J.P. Morgan based upon an analysis of the weighted average cost of capital of Atkore. The present values of the unlevered free cash flow estimates and the range of terminal values were then adjusted for Atkore’s estimated net debt of $486 million as of June 26, 2026 and the value of Atkore’s net operating losses. This analysis indicated a range of implied per share equity value for the Common Stock (rounded to the nearest $0.25) of $84.25 to $119.50, which J.P. Morgan compared to (i) the closing share price of the Common Stock of $72.96 as of July 31, 2026 and (ii) the Merger Consideration of $95.00.

The foregoing summary of certain material financial analyses does not purport to be a complete description of the analyses or data presented by J.P. Morgan. The preparation of a fairness opinion is a complex process and is not necessarily susceptible to partial analysis or summary description. J.P. Morgan believes that the foregoing summary and its analyses must be considered as a whole and that selecting portions of the foregoing summary and these analyses, without considering all of its analyses as a whole, could create an incomplete view of the processes underlying the analyses and its opinion. As a result, the ranges of valuations resulting from any particular analysis or combination of analyses described above were merely utilized to create points of reference for analytical purposes and should not be taken to be the view of J.P. Morgan with respect to the actual value of Atkore. The order of analyses described does not represent the relative importance or weight given to those analyses by J.P. Morgan. In arriving at its opinion, J.P. Morgan did not attribute any particular weight to any analyses or factors considered by it and did not form an opinion as to whether any individual analysis or factor (positive or negative), considered in isolation, supported or failed to support its opinion. Rather, J.P. Morgan considered the totality of the factors and analyses performed in determining its opinion. Analyses based upon forecasts of future results are inherently uncertain, as they are subject to numerous factors or events beyond the control of the parties and their advisors. Accordingly, forecasts and analyses used or made by J.P. Morgan are not necessarily indicative of actual future results, which may be significantly more or less favorable than suggested by those analyses. Moreover, J.P. Morgan’s analyses are not and do not purport to be appraisals or otherwise reflective of the prices at which businesses actually could be acquired or sold. None of the selected companies reviewed as described in the above summary is identical to Atkore, and none of the selected transactions reviewed was identical to the Merger. However, the companies selected were chosen because they are publicly traded companies with operations and businesses that, for purposes of J.P. Morgan’s analysis, may be considered similar to those of Atkore. The transactions selected were similarly chosen because certain aspects of the transactions, for purposes of J.P. Morgan’s analysis, may be considered similar to the Merger. The analyses necessarily involve complex considerations and judgments concerning differences in financial and operational characteristics of the companies involved and other factors that could affect the companies compared to Atkore and the transactions compared to the Merger.

As a part of its investment banking business, J.P. Morgan and its affiliates are continually engaged in the valuation of businesses and their securities in connection with mergers and acquisitions, investments for passive and control purposes, negotiated underwritings, secondary distributions of listed and unlisted securities, private

placements, and valuations for corporate and other purposes. J.P. Morgan was selected to advise Atkore with respect to the Merger and deliver an opinion to the Board with respect to the Merger on the basis of, among other things, such experience and its qualifications and reputation in connection with such matters and its familiarity with Atkore and the industries in which it operates.

For financial advisory services rendered in connection with the Merger, Atkore has agreed to pay J.P. Morgan an estimated fee of approximately $21.5 million, $3 million of which became payable to J.P. Morgan at the time J.P. Morgan delivered its opinion and the remainder of which is contingent and payable upon the consummation of the Merger. In addition, Atkore has agreed to reimburse J.P. Morgan for certain of its expenses incurred in connection with its services, including the fees and disbursements of counsel, and will indemnify J.P. Morgan against certain liabilities arising out of J.P. Morgan’s engagement.

During the two years preceding the date of J.P. Morgan’s written opinion, J.P. Morgan and its affiliates have had commercial or investment banking relationships with Atkore or its affiliates, for which J.P. Morgan and such affiliates have received customary compensation. Such services during such period have included acting as joint lead arranger and joint bookrunner on a credit facility in April 2025. During the two years preceding the date of J.P. Morgan’s written opinion, J.P. Morgan and its affiliates have had commercial or investment banking relationships with Prysmian or its affiliates, for which J.P. Morgan and such affiliates have received customary compensation. Such services during such period have included acting as joint lead manager on a bond issuance in May 2025. During the two years preceding the date of J.P. Morgan’s written opinion, the aggregate fees recognized by J.P. Morgan from Atkore and Prysmian were approximately $2 million and $61.5 million respectively. In addition, J.P. Morgan’s commercial banking affiliate is an agent bank and a lender under outstanding credit facilities of Atkore, for which it receives customary compensation or other financial benefits. In addition, J.P. Morgan and its affiliates hold, on a proprietary basis, less than 1% of the outstanding Common Stock. In addition, J.P. Morgan and/or its affiliates are currently providing services to Prysmian and/or certain of its affiliates, which services are unrelated to the Merger. J.P. Morgan expects to receive customary compensation in connection with such services which, considered in the aggregate and assuming all the transactions are actually completed, are expected by J.P. Morgan as of the date hereof to be less than the fees that it would receive from Atkore if the Merger were consummated. In the ordinary course of their businesses, J.P. Morgan and its affiliates may actively trade the debt and equity securities or financial instruments (including derivatives, bank loans or other obligations) of Atkore or Prysmian for their own account or for the accounts of customers and, accordingly, may at any time hold long or short positions in such securities or other financial instruments.

Atkore does not, as a matter of course, publicly disclose long-term projections as to future revenue, earnings or other results and is especially cautious of making financial forecasts for extended periods given, among other reasons, the uncertainty, unpredictability and subjectivity of the underlying assumptions and estimates. As a result, Atkore does not endorse projections or other unaudited prospective financial information as necessarily indicative of actual future results. However, in connection with the Board’s evaluation of a potential transaction, Atkore’s management prepared certain unaudited prospective financial information for fiscal years 2026 through 2030 (the “Prospective Financial Information”).

The Prospective Financial Information was not prepared with a view to public disclosure and is included in this proxy statement only because such information was (i) made available, in part, to potential counterparties, including Prysmian, and certain of their respective representatives in connection with such counterparties’ due diligence review of Atkore and (ii) provided to and reviewed with the Board in connection with its evaluation of the Merger Agreement and the transactions contemplated thereby, including the Merger. The Prospective Financial Information was approved by the Board for Citi’s and J.P. Morgan’s use and reliance in connection with their respective financial analyses and opinions, as described in the section titled “—Opinions of Atkore’s Financial Advisors.”

The Prospective Financial Information was not prepared with a view to compliance with U.S. Generally Accepted Accounting Principles (“GAAP”). Non-GAAP financial measures should not be considered in isolation from, or as a substitute for, financial information presented in compliance with GAAP, and non-GAAP financial measures, as used in the Prospective Financial Information, may not be comparable to similarly titled amounts used by other companies or persons. Financial measures provided to a board of directors or a financial advisor in connection with a proposed business combination are excluded from the definition of non-GAAP financial measures and therefore, are not subject to SEC rules regarding disclosures of non-GAAP financial measures, which would

otherwise require a reconciliation of a non-GAAP financial measure to a GAAP financial measure. Accordingly, Atkore has not provided a reconciliation of the financial measures included in the Prospective Financial Information.

In addition, the Prospective Financial Information was not prepared with a view to compliance with the published guidelines of the SEC regarding projections and forward-looking statements or the guidelines established by the American Institute of Certified Public Accountants for preparation and presentation of prospective financial information. The Prospective Financial Information has been prepared by, and is the responsibility of, Atkore’s management. Neither Atkore’s independent auditors, nor any other independent accountants, have compiled, examined, or performed any procedures with respect to the Prospective Financial Information, nor have they expressed any opinion or any other form of assurance on such information or its achievability, and assume no responsibility for, and disclaim any association with, the Prospective Financial Information.

The following is a summary of the Prospective Financial Information:

Although this summary of the Prospective Financial Information is presented with numerical specificity, the projections reflect numerous variables, assumptions and estimates as to future events made by Atkore’s management that Atkore’s management believed were reasonable at the time the Prospective Financial Information was prepared, taking into account the relevant information available to Atkore’s management at the time. Since the Prospective Financial Information covers multiple years, it becomes subject to greater uncertainty with each successive year. Various assumptions underlying the Prospective Financial Information may not prove to be reflective of actual results. The assumptions upon which the Prospective Financial Information were based necessarily involve judgments with respect to, among other things, future economic, competitive and regulatory conditions and financial market conditions, all of which are difficult or impossible to predict and many of which are beyond Atkore’s control. The Prospective Financial Information also reflects assumptions as to certain business strategies or plans that are subject to change. Furthermore, the Prospective Financial Information does not take into account any circumstances or events occurring after the date it was prepared, including the announcement of the Merger Agreement. The projections in the Prospective Financial Information may not be realized, and actual results may be significantly higher or lower than projected in the Prospective Financial Information. Important factors that may affect actual results and cause projections in the Prospective Financial Information to not be achieved include, but are not limited to, risks and uncertainties relating to the business of Atkore (including its ability to achieve strategic goals, objectives and targets over the applicable periods), industry performance, the regulatory and competitive environment, general business and economic conditions and other risk factors described in the section titled “Cautionary Statement Regarding Forward-Looking Statements.”

The Prospective Financial Information included in this proxy statement is subjective and should not be regarded as an indication that Atkore or any of its affiliates, advisors or representatives, or any other persons, have considered the Prospective Financial Information to be necessarily predictive of actual future events, or that it should be construed as financial guidance, and the Prospective Financial Information should not be relied upon as such. Except to the extent required by applicable federal securities laws, Atkore does not intend to, and expressly disclaims any responsibility for, updating or otherwise revising or reconciling the Prospective Financial Information to reflect (i) circumstances existing after the date when the Prospective Financial Information was prepared or (ii) the occurrence of future events or changes in general economic or industry conditions, even in the event that any of the assumptions underlying the Prospective Financial Information are shown to no longer be appropriate. Neither Atkore nor any of its affiliates, advisors or representatives, nor any other person, makes any representation to any person regarding the ultimate performance of Atkore relative to the financial forecasts reflected in the Prospective Financial Information by virtue of its inclusion in this proxy statement.

This summary of the Prospective Financial Information is not being included in this proxy statement to influence your decision whether to vote in favor of the Merger Proposal, the Compensation Proposal, the Adjournment Proposal or any other proposal that may be voted upon at the Special Meeting. In light of the foregoing factors and the uncertainties inherent in these forecasts, you are cautioned not to place undue reliance on the Prospective Financial Information.

Atkore’s directors and executive officers have interests in the Merger that may be different from, or in addition to, the interests of Atkore stockholders generally and these interests may create potential conflicts of interest. You should keep this in mind when considering the recommendation of the Board “FOR” the Merger Proposal and “FOR” the Compensation Proposal. The Board was aware of these interests and considered them, among other matters, when evaluating and negotiating the Merger Agreement, in approving the Merger Agreement and the Merger and in making its recommendation. The Merger will constitute a “change in control” for purposes of the Atkore executive compensation and benefit plans described below. These interests may include, among others, those described in this section and the section titled “—Quantification of Potential Payments and Benefits to Atkore’s Named Executive Officers in Connection with the Merger.”

For purposes of this disclosure, Atkore’s non-employee directors are: Michael V. Schrock; Franklin S. Edmonds, Jr.; B. Joanne Edwards; Jeri L. Isbell; Wilbert W. James, Jr.; Justin A. Kershaw; Scott H. Muse; Betty R. Wynn; and A. Mark Zeffiro.

For purposes of this disclosure, Atkore’s executive officers who are named executive officers are: William E. Waltz, Jr., President and Chief Executive Officer, Director; John M. Deitzer, Vice President, Chief Financial Officer; John W. Pregenzer, Chief Operating Officer and President, Electrical Business Unit; Daniel S. Kelly, Vice President, General Counsel & Corporate Secretary; and Mark F. Lamps, President, Safety & Infrastructure Business Unit.

In accordance with SEC rules, this disclosure also covers individuals who are not named executive officers but who served as executive officers of Atkore at any time since October 1, 2024 and who have interests in the Merger. Accordingly, for purposes of this disclosure, Atkore’s executive officers who are not named executive officers are: James W. Alvey, Vice President, Chief Accounting Officer; and LeAngela W. Lowe, Vice President, Chief Human Resources Officer.

The following assumptions were used solely for purposes of quantifying the potential payments and benefits described in this section and the potential payments and benefits described in the below section titled “—Quantification of Potential Payments and Benefits to Atkore’s Named Executive Officers in Connection with the Merger”:

The amounts quantified in this section, including in the below section titled “—Quantification of Potential Payments and Benefits to Atkore’s Named Executive Officers in Connection with the Merger,” are estimates based on multiple assumptions, including the assumptions described above, that may or may not actually occur or be accurate as of the relevant date and do not reflect or attempt to forecast certain compensation actions that may occur before completion of the Merger but following the date of this proxy statement, including any additional equity award grants, issuances or forfeitures that may occur prior to the completion of the Merger. Accordingly, the actual amounts, if any, that will or may be paid or become payable to Atkore’s directors and executive officers may materially differ from such estimates. All amounts are rounded to the nearest whole number.

Set forth below is a discussion of the Company RSUs, Company PSUs, Company Options and Company DSUs held by Atkore’s non-employee directors and executive officers. These equity-based awards were granted pursuant to the Atkore International Group Inc. 2020 Omnibus Incentive Plan, the Atkore International Group Inc. 2016 Omnibus Incentive Plan and the Atkore International Group Inc. Stock Incentive Plan (each such plan, together with all award agreements thereunder, an “Atkore Stock Plan”).

Treatment of Equity-Based Awards in the Merger

Atkore equity-based awards that are outstanding as of immediately prior to the Effective Time, including those held by Atkore non-employee directors and executive officers, will be treated as described in the section titled “The Merger Agreement—Merger Consideration—Treatment of Atkore Equity Awards.” This treatment is also summarized below. Pursuant to the Merger Agreement:

The following table summarizes the estimated cash value of the Company RSUs and Company DSUs held by each non-employee director as of the Assumed Closing Date, based on the assumptions set forth above and made solely for purposes of this proxy statement (including that each share of Common Stock underlying outstanding equity-based awards is entitled to receive the Merger Consideration).

As of the Assumed Closing Date, Atkore’s executive officers held Company RSUs, Company PSUs and Company Options having an aggregate cash value (calculated assuming that each share of Common Stock underlying outstanding equity-based awards is entitled to receive the Merger Consideration) of $13,469,937, $11,603,086 and $21,764,547, respectively (including, in each case, unvested awards and awards that have vested but not yet settled into, or been exercised for, shares of Common Stock). The aggregate cash value of Company PSUs outstanding is calculated by determining the number of shares of Common Stock that would be subject to each award at the Assumed Closing Date according to the terms of such awards (as described further below).

The following table summarizes the vested and unvested equity-based awards held by each executive officer as of the Assumed Closing Date and the estimated cash value that each executive officer would be entitled to receive in respect of such awards based on the assumptions described above and made solely for purposes of this proxy statement (including that each share of Common Stock underlying outstanding equity-based awards is entitled to receive the Merger Consideration).

For information regarding the number of shares of Common Stock held by Atkore executive officers and non-employee directors, see the section of this proxy statement titled “Security Ownership of Certain Beneficial Owners and Management.”

None of Atkore’s executive officers are currently party to an employment agreement or offer letter that governs the terms of their post-termination compensation. Each of Atkore’s named executive officers and Ms. Lowe are participants in the Executive Severance Policy. Post-termination compensation for Mr. Alvey is governed by Atkore’s general severance policy (the “General Severance Policy”), as described below.

Under the Executive Severance Policy, a participant is entitled to receive severance payments and termination benefits upon a termination of the participant’s employment by Atkore without “cause” or by the participant with “good reason” (each, a “Qualifying Termination”), with enhanced severance benefits payable if a participant experiences a Qualifying Termination within 24 months following a “change in control” (including the consummation of the Merger). These payments and termination benefits include:

The severance multiples under the Executive Severance Policy depend on whether the participant’s Qualifying Termination occurs before or within 24 months after a change in control (including the consummation of the Merger). Given that, for purposes of this proxy statement, each executive officer that participates in the Executive Severance Policy is deemed to be have experienced a Qualifying Termination immediately following the Assumed Closing Date, the change in control multiple would apply. The applicable severance multiple for each executive officer who participates in the Executive Severance Policy is as follows, depending on the time of the Qualifying Termination:

If the severance payment is paid in connection with a Qualifying Termination following a change in control, it will be paid in a lump sum to the maximum extent practicable under applicable law. For any other Qualifying Termination, the severance payment is paid in equal installments over the applicable severance period. Executive officers are also generally eligible for customary outplacement services in connection with a Qualifying Termination.

If any payments or benefits to a participant under the Executive Severance Policy would result in “golden parachute” excise taxes under Section 4999 of the Internal Revenue Code of 1986, as amended (the “Code”), such payments and benefits would be reduced to an amount that would not result in the imposition of such tax if the reduction would be better for the participant on a net after-tax basis. No employee is entitled to be made whole for these taxes under any circumstances. In order to receive the severance payments and termination benefits under the Executive Severance Policy, the participant must execute a release of claims and comply with the applicable restrictive covenants described below.

Under the General Severance Policy, Mr. Alvey is entitled to receive severance payments and termination benefits upon a termination other than for “cause” of his employment by Atkore under specific circumstances specified in the General Severance Policy, regardless of whether a change in control (including the consummation of the Merger) has occurred. These payments and termination benefits include:

The severance payment will be paid in a lump sum. In order to receive the severance payments and termination benefits under the General Severance Policy, a participant must execute a release of claims and a non-compete agreement.

Atkore has entered into a retention award letter with Mr. Alvey, effective as of August 7, 2026, pursuant to which he will be eligible to receive a cash retention award approved by the Human Resources and Compensation Committee of the Board (the “Compensation Committee”). The retention award is intended to recognize and incentivize his contributions to the success of the Merger. The retention award value is $226,744, of which one-third will vest 30 days following the consummation of the Merger, and the remaining two-thirds will vest on December 31, 2027, in each case, subject to continued employment through the applicable date. In the event that Mr. Alvey’s employment is terminated without “cause” (as defined in the retention award letter) then, subject to his execution of a customary release of claims, he will become vested in any unvested amount of his retention award. As of the date hereof, Atkore has not, and does not intend to, enter into retention award letter with any of its other executive officers.

Pursuant to the Executive Severance Policy, each participant is subject to non-competition and non-solicitation of customers and employees covenants that apply for the number of months following the applicable participant’s termination of employment equal to the applicable severance multiple (e.g., 18 months for a 1.5-year severance multiple), as well as perpetual confidentiality and non-disparagement clauses.

In addition, all executive officers are subject to the restrictive covenants contained in their equity award agreements under the Atkore Stock Plans. Such awards generally include non-competition covenants that apply for one year following the applicable executive officer’s termination of employment, non-solicitation covenants that apply for up to two years following the applicable executive officer’s termination of employment, as well as perpetual confidentiality clauses.

The Merger Agreement provides that any employee of Atkore who continues to be an employee of the surviving corporation in the Merger following the consummation of the Merger, including any of Atkore’s executive officers, will receive a pro rata portion of the annual bonus for the fiscal year of the consummation of the Merger in an amount determined assuming (i) with respect to any applicable individual performance goals, that such goals are achieved at no less than target levels of performance and (ii) with respect to any applicable Company performance goals, that such goals are achieved at the greater of (x) target performance and (y) actual performance as of the Closing Date (as determined by Atkore in good faith immediately prior to the Closing), and pro-rated by a fraction, the numerator of which is the number of days elapsed in the fiscal year prior to the Effective Time, and the denominator of which is 365 (the “Pro Rata Bonus Payment”). The Pro Rata Bonus Payment will be payable at the same time and subject to the same terms and conditions as called for in the applicable bonus plan in effect at the Effective Time. If any participant in the Executive Severance Policy experiences a termination without “cause” prior to the applicable payment date, he or she will not be eligible for the Pro Rata Bonus Payment and will instead receive the pro-rated annual bonus provided in the Executive Severance Policy.

As of the date of this proxy statement, none of our executive officers have entered into any agreement with Prysmian or any of its affiliates regarding continued employment with Prysmian, the surviving corporation in the Merger or one or more of their affiliates, although it is possible that Prysmian may enter into new employment or other arrangement with our executive officers in the future. In addition, pursuant to the Merger Agreement, as described in the section below titled “The Merger Agreement—Certain Employee Matters,” Prysmian has agreed that it will cause the surviving corporation to provide, for a period of 12 months following the Effective Time, certain levels of compensation and benefits to each individual who is employed by Atkore or any of its subsidiaries as of the Effective Time and continues to be employed by the surviving corporation or any of its subsidiaries as of immediately following the Effective Time.

The Merger Agreement provides for certain indemnification arrangements for Atkore’s current and former officers and directors and certain other indemnified persons, and the continuation of certain insurance arrangements, in each case for six years after the Effective Time.

Upon Closing, Atkore’s stockholders pursuing litigation claims derivatively on behalf of Atkore against certain of Atkore’s current and former officers and directors will lose standing to maintain those claims. As a result, Atkore’s officers and directors who are defendants may benefit from either the dismissal of existing litigation and/or Prysmian’s assuming control of any and all of Atkore’s current or potential litigation claims. For additional information, see the section titled “—Legal Proceedings.”

This section sets forth the information required by Item 402(t) of Regulation S-K regarding the compensation for each of Atkore’s named executive officers that is based on or otherwise relates to the Merger. The Merger-related compensation payable to these individuals is subject to a non-binding advisory vote of Atkore stockholders, as described in the section titled “Proposals for the Special Meeting—The Compensation Proposal.”

The table below sets forth estimates of the amounts of payments and benefits that each of Atkore’s named executive officers would receive in connection with the Merger using the assumptions described above under “—Interests of Atkore’s Directors and Executive Officers in the Merger—Certain Assumptions.” The amounts quantified in this section are estimates based on multiple assumptions that may or may not actually occur or be accurate as of the relevant date. These amounts also do not reflect any compensation actions that may occur after the date of this proxy statement and before completion of the Merger. Further, the table below assumes no reduction in payments or benefits for the purposes of the excise tax under Section 4999 of the Code. Accordingly, the actual amounts, if any, that will or may be paid or become payable to our named executive officers may materially differ from such estimates. All amounts are rounded to the nearest whole number.

The consummation of the Merger is not conditioned on Prysmian’s receipt of any financing.

In connection with its entry into the Merger Agreement, on July 29, 2026, Prysmian entered into a debt commitment letter. Pursuant to such debt commitment letter, certain lenders have committed, on the terms and subject to the conditions set forth therein, to provide debt financing to Prysmian in an aggregate amount sufficient to fund the consummation of the transactions contemplated by the Merger Agreement and the fees, commissions, costs and expenses incurred in connection therewith.

Under Section 262 of the DGCL, if the Merger is completed and certain conditions under Section 262(g) of the DGCL are satisfied, holders of record and beneficial owners of shares of Common Stock who (i) have delivered a written demand for appraisal of such holder’s or owner’s shares of Common Stock in compliance with Section 262 of the DGCL to Atkore prior to the vote on the Merger Proposal, (ii) do not vote, in person or by proxy, in favor of the Merger Proposal, (iii) continuously hold of record or beneficially own such shares on the date of making the demand for appraisal through the Effective Time, and (iv) otherwise comply with the statutory requirements set forth in Section 262 of the DGCL are entitled to have their shares of Common Stock appraised by the Delaware Court of Chancery and to receive payment in cash, in lieu of the Merger Consideration, for the “fair value” of their shares of Common Stock, exclusive of any element of value arising from the accomplishment or expectation of the Merger, together with (unless the Delaware Court of Chancery in its discretion determines otherwise for good cause shown) interest, if any, on the amount determined by the Delaware Court of Chancery to be the “fair value.” The “fair value” of such shares of Common Stock, as determined by the Delaware Court of Chancery, may be less than, equal to or more than the Merger Consideration. A holder of record or beneficial owner of shares of Common Stock must satisfy the requirements of Section 262 of the DGCL to exercise and perfect appraisal rights and follow precisely the statutory procedures pursuant to Section 262 of the DGCL in a timely manner. Failure to comply strictly with these procedures will result in a loss of appraisal rights. These procedures are described in the section titled “Appraisal Rights” and Section 262 of the DGCL, which governs such rights and procedures and may be accessed without subscription or cost at https://delcode.delaware.gov/title8/c001/sc09/index.html#262 and is incorporated by reference herein.

Atkore will cooperate with Prysmian and use its reasonable best efforts to cause the Common Stock to be delisted from the NYSE and deregistered under the Exchange Act as promptly as practicable following the Effective Time. If the Merger is completed, the Common Stock will be delisted from the NYSE and deregistered under the Exchange Act, and Atkore will no longer be required to file periodic reports with the SEC on account of the Common Stock.

The following is a general discussion of the material U.S. federal income tax consequences of the Merger to U.S. holders (as defined below) that exchange their shares of Common Stock for cash pursuant to the Merger. This discussion is based on the Code, U.S. Treasury Regulations promulgated under the Code, judicial decisions, and published guidance of the Internal Revenue Service (the “IRS”), all as in effect as of the date hereof and all of which are subject to change or differing interpretations, possibly with retroactive effect. Any such change or differing interpretation could affect the statements set forth in this discussion. This discussion is not binding on the IRS or a court and there can be no assurance that the tax consequences described herein will not be challenged by the IRS or that they would be sustained by a court if so challenged. This summary is based upon the assumption that the Merger will be consummated in accordance with the Merger Agreement and as described elsewhere in this proxy statement.

This discussion is for general informational purposes only and does not constitute tax advice. This discussion is limited to U.S. holders of Common Stock that hold their shares of Common Stock as a “capital asset” within the meaning of Section 1221 of the Code (generally, property held for investment). This is not a complete summary of all of the tax consequences of the Merger and it does not address all aspects of U.S. federal income taxation that may be relevant to particular holders of Common Stock in light of their particular circumstances, nor does it address tax considerations applicable to holders of Common Stock that are or may be subject to special treatment under the U.S. federal income tax laws (such as, without limitation, non-U.S. holders, banks or other financial institutions, insurance companies, mutual funds, certain former U.S. citizens or long-term residents of the United States, dealers in stocks, securities, commodities or currencies, traders in securities who elect to apply a mark-to-market method of accounting, insurance companies, private foundations, private university endowments and other tax-exempt holders, governments or governmental organizations, real estate investment trusts, regulated investment companies, holders that hold their Common Stock in a retirement or other tax-advantaged account, holders required to accelerate the recognition of any item of gross income as a result of such income being recognized on an applicable financial statement, controlled foreign corporations, passive foreign investment companies, partnerships (or other entities or arrangements treated as partnerships for U.S. federal income tax purposes) or other pass-through entities (including

S Corporations) or owners thereof, holders who hold their Common Stock as part of a “hedge,” “straddle,” “conversion,” “synthetic security,” “integrated investment” or “constructive sale” transaction or other risk reduction transaction, persons who, actually or constructively, own or have owned 5% or more of the equity interests in Atkore (by vote or value) or will own 5% or more of the equity interests in Prysmian after the Merger, U.S. expatriates or former long-term residents of the United States, holders whose functional currency is not the U.S. dollar and holders who acquired Common Stock upon the exercise of employee stock options or otherwise as compensation). In addition, this summary does not address any tax consequences arising under the alternative minimum tax, the Medicare tax on net investment income or the Foreign Account Tax Compliance Act of 2010 (including the U.S. Treasury Regulations and other administrative guidance promulgated thereunder and intergovernmental agreements entered pursuant thereto or in connection therewith), any estate, gift or other non-income tax consequences or any state, local or foreign tax consequences.

If an entity or arrangement treated as a partnership for U.S. federal income tax purposes holds Common Stock, the U.S. federal income tax consequences of the Merger to such partnership or any person treated as a partner in such partnership for U.S. federal income tax purposes generally will depend in part upon the status and activities of such partnership and each particular partner. Holders of Common Stock that are partnerships and partners in such partnerships for U.S. federal income tax purposes should consult their own tax advisors regarding the U.S. federal income tax consequences of the Merger.

For purposes of this discussion, a U.S. holder is a beneficial owner of Common Stock that is, for U.S. federal income tax purposes:

For purposes of this discussion, a non-U.S. holder is any beneficial owner of Common Stock that is neither a U.S. holder nor an entity treated as a partnership for U.S. federal income tax purposes.

THE FOLLOWING IS A GENERAL DISCUSSION OF THE MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGER UNDER CURRENT LAW, IS FOR GENERAL INFORMATION ONLY, AND IS NOT INTENDED TO BE, AND SHOULD NOT BE CONSTRUED AS, TAX ADVICE. THE SPECIFIC TAX CONSEQUENCES OF THE MERGER TO ANY PARTICULAR HOLDER WILL DEPEND ON SUCH HOLDER’S PARTICULAR FACTS AND CIRCUMSTANCES AND TAX STATUS. ALL HOLDERS SHOULD CONSULT THEIR OWN TAX ADVISORS AS TO THE PARTICULAR TAX CONSEQUENCES OF THE MERGER TO THEM, INCLUDING THE APPLICATION AND EFFECT OF U.S. FEDERAL, STATE, LOCAL, NON-U.S. AND OTHER TAX LAWS.

The exchange of Common Stock for cash pursuant to the Merger will be a taxable transaction for U.S. federal income tax purposes. In general, a U.S. holder who exchanges shares of Common Stock for cash in the Merger will recognize gain or loss for U.S. federal income tax purposes in an amount equal to the difference, if any, between (i) the amount of cash received and (ii) such U.S. holder’s adjusted tax basis in the Common Stock exchanged therefor. Generally, any such gain or loss will be capital gain or loss and will be long-term capital gain or loss if the Common Stock exchanged was held for more than one year as of the closing date of the Merger. Long-term capital gains of certain non-corporate U.S. holders generally are subject to U.S. federal income tax at preferential rates. The deductibility of capital losses is subject to limitations. If a U.S. holder acquired different blocks of Common Stock at different times or at different prices, gain or loss must be determined separately with respect to each block of Common Stock.

Information reporting and backup withholding (currently, at a rate of 24%) may apply to payments to a holder pursuant to the Merger. Backup withholding generally will not apply to a U.S. holder that furnishes a correct taxpayer identification number and certifies that such U.S. holder is not subject to backup withholding on an IRS Form W-9 or otherwise establishes an exemption from backup withholding. Backup withholding is not an additional tax. Amounts withheld under the backup withholding rules may be refunded or credited against a holder’s U.S. federal income tax liability, if any, provided that the required information is timely furnished to the IRS.

THE FOREGOING IS A GENERAL DISCUSSION OF THE MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGER UNDER CURRENT LAW, IS FOR GENERAL INFORMATION ONLY, AND IS NOT INTENDED TO BE, AND SHOULD NOT BE CONSTRUED AS, TAX ADVICE. THE SPECIFIC TAX CONSEQUENCES OF THE MERGER TO ANY PARTICULAR HOLDER WILL DEPEND ON SUCH HOLDER’S PARTICULAR FACTS AND CIRCUMSTANCES AND TAX STATUS. ALL HOLDERS SHOULD CONSULT THEIR OWN TAX ADVISORS AS TO THE PARTICULAR TAX CONSEQUENCES OF THE MERGER TO THEM, INCLUDING THE APPLICATION AND EFFECT OF U.S. FEDERAL, STATE, LOCAL, NON-U.S. AND OTHER TAX LAWS.

Atkore and Prysmian have agreed to use their respective reasonable best efforts to take all actions necessary, proper or advisable under applicable law to consummate and make effective the Merger as promptly as practicable after the date of the Merger Agreement, including to obtain the required regulatory approvals for the Merger, and Prysmian has agreed to use reasonable best efforts to take all actions necessary to avoid or eliminate regulatory impediments to the Merger so as to enable the closing of the Merger to occur as promptly as practicable, including agreeing to specified divestitures and other remedial actions affecting Atkore’s business, subject to negotiated limitations. For a summary of such actions, see “The Merger Agreement—Covenants and Agreements.”

Under the HSR Act, the Merger may not be completed until certain information and materials have been provided by Atkore and Prysmian to the Antitrust Division and the FTC, and the applicable waiting period under the HSR Act (or any extension thereof) has expired or been terminated. The parties filed the required HSR Act notifications with the Antitrust Division and the FTC on August 14, 2026. On that basis, the applicable waiting period under the HSR Act is expected to expire at 11:59 p.m. Eastern Time on September 14, 2026, unless earlier terminated by the FTC.

The Merger will entail pre-closing filings to national merger control authorities in Austria, Australia and Canada. Under jurisdiction-specific laws, the Merger Agreement would require Prysmian and Atkore to submit notifications to the antitrust authorities of each of these countries prior to the closing date of the Merger, and antitrust authorities thereof would have jurisdiction to conduct staged reviews, request information, pause their review, and issue governmental orders that could prohibit the Merger. The transactions contemplated by the Merger Agreement cannot be completed until Prysmian and Atkore obtain all necessary clearances or the applicable waiting periods have expired or been terminated in each of these jurisdictions.

The Antitrust Division, the FTC, and foreign antitrust authorities frequently scrutinize the legality of transactions, such as the Merger, under the Antitrust Laws. At any time before or after the Merger, the Antitrust Division, the FTC or a foreign antitrust authority could take action under the Antitrust Laws as it deems necessary or desirable in the public interest, including seeking to enjoin the Merger or seeking divestiture of substantial businesses or assets of Atkore, Prysmian or their respective affiliates. Private parties may also bring legal actions under the Antitrust Laws in certain circumstances. There can be no assurance that a challenge to the Merger on antitrust grounds will not be made or, if a challenge is made, of the result.

The Merger Agreement provides until August 2, 2027 to achieve the necessary regulatory clearances, subject to an automatic extension to November 2, 2027 if, on August 2, 2027, all other applicable closing conditions have been satisfied or waived and any closing condition related to regulatory approvals or law or governmental orders (solely

in connection with any antitrust law or foreign regulatory law) has not been satisfied or waived, and a further automatic extension to February 2, 2028 if such regulatory conditions remain unsatisfied or unwaived as of November 2, 2027 and the other applicable closing conditions have been satisfied or waived. The Merger Agreement provides that Prysmian is not obligated to proffer or agree to any divestiture or other remedy with respect to assets or businesses of Prysmian or any of its pre-Closing affiliates or specified assets or businesses of Atkore. Under the Merger Agreement, Atkore is not obligated to agree to any divestiture or other remedy not conditioned on the consummation of the Closing.

As of the date of this proxy statement, there are pending stockholder derivative claims for breach of fiduciary duties and related claims against certain current and former Atkore directors and officers, based primarily on allegations in pending antitrust and securities litigation regarding PVC pipe pricing (as further described in the section titled “—Background of the Merger”). The claims seek recovery of $186.5 million Atkore paid to settle certain matters in the Antitrust Litigation, as well as additional defense costs and liabilities for other pending Antitrust and Related Matters. These derivative claims belong to Atkore, not to the individual stockholders who have asserted them, and any potential recovery would flow to Atkore and not to any individual stockholder. Under Delaware law, only current stockholders can pursue a derivative claim. Upon Closing, Atkore’s stockholders will cease to be stockholders of Atkore and, as a result, would no longer have standing to pursue the derivative claims. All of the derivative claims would remain assets of Atkore, and Prysmian would control the decision whether to pursue, settle, or abandon such claims and would receive any potential recovery from them.

More specifically, stockholders have filed derivative litigation and have made demands on the Board to investigate and to sue current and former directors and officers of Atkore. The derivative litigation has been stayed in an early stage. In response to the demands, the Board established a review committee (the “Review Committee”) to investigate the allegations and evaluate whether it is in Atkore’s best interests to sue any current or former directors or officers. The Review Committee consists of three outside directors, Ms. Edwards, Ms. Wynn, and Mr. Kershaw, and it has retained independent counsel. The Review Committee’s investigation remains ongoing. It has not yet reached conclusions or made recommendations to the Board.

You are encouraged to read the description of Atkore’s legal proceedings contained in the documents that are incorporated by reference into this proxy statement, including in “Item 3. Legal Proceedings” in Atkore’s Annual Report on Form 10-K for the fiscal year ended September 30, 2025 and “Part II, Item 1. Legal Proceedings” in Atkore’s Quarterly Report on Form 10-Q for the quarter ended June 26, 2026. See “Where You Can Find More Information.”

This section describes the material provisions of the Merger Agreement, but it does not describe all of the terms of the Merger Agreement. The following summary is qualified in its entirety by reference to the complete text of the Merger Agreement, a copy of which is attached as Annex A, and which is incorporated by reference into this proxy statement. This summary does not purport to be complete and may not contain all of the information about the Merger Agreement that is important to you. The rights and obligations of Atkore, Prysmian, Merger Sub and Guarantor are governed by the express terms and conditions of the Merger Agreement and not by this summary or any of the other information contained in this proxy statement. You are encouraged to read the Merger Agreement carefully and in its entirety because it is the legal document that governs the Merger. This summary is not intended to provide any other factual information about Atkore, Prysmian, Merger Sub, Guarantor or any of their respective subsidiaries or affiliates. Information about Atkore, Prysmian, Merger Sub and Guarantor can be found elsewhere in this proxy statement and in the documents incorporated by reference herein. See also “Where You Can Find More Information.”

The Merger Agreement contains representations, warranties and covenants by each of the parties to the Merger Agreement, which were made only for purposes of the Merger Agreement, as of specified dates. The representations, warranties and covenants in the Merger Agreement were made solely for the benefit of the parties to the Merger Agreement, are subject to limitations agreed upon by the contracting parties, including being qualified by publicly available information and confidential disclosures made between the parties, and may be subject to standards of materiality applicable to the contracting parties that differ from those applicable to investors or from those generally applicable to reports and documents filed with the SEC. It is important to bear in mind that the representations and warranties were made solely for the benefit of the parties to the Merger Agreement and were negotiated for the purpose of allocating contractual risk among the parties to the Merger Agreement rather than to establish matters as facts. Therefore, investors should not rely on representations, warranties and covenants or any descriptions thereof as characterizations of the actual state of facts or condition of Atkore, Prysmian, Merger Sub, Guarantor or any of their respective subsidiaries or affiliates. Moreover, information concerning the subject matter of the representations, warranties and covenants contained in the Merger Agreement or any other agreement between such parties or their affiliates may change and may have changed after the date of each such agreement (or the date on which such representations and warranties were made), which subsequent information may or may not be fully reflected in Atkore’s or Prysmian’s public disclosures or the public disclosures of any of their respective subsidiaries or affiliates. In addition, investors should not rely on the covenants in the Merger Agreement as actual limitations on the respective businesses of Atkore, Prysmian, Merger Sub or Guarantor, because the parties may take certain actions that are either expressly permitted in the confidential disclosures to the Merger Agreement or as otherwise consented to by the appropriate party, which consent may be given without prior notice to the public. The representations and warranties in the Merger Agreement generally do not survive the completion of the Merger. Investors are not third-party beneficiaries under the Merger Agreement except for the limited purposes expressly set forth therein and should not rely on the representations and warranties or any descriptions thereof as characterizations of the actual state of facts or condition of the parties thereto or any of their respective subsidiaries or affiliates. The representations, warranties, covenants and other agreements in the Merger Agreement should not be read alone, but should instead be read in conjunction with the other information regarding the Merger Agreement, the Merger, Atkore, Prysmian and their respective affiliates and businesses (including the foregoing explanation), which is contained in, or incorporated by reference into, this proxy statement (including the annexes hereto), as well as in the Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, and other filings that Atkore has made or will make with the SEC. See “Where You Can Find More Information.”

Pursuant to the terms of the Merger Agreement, at the Effective Time, Merger Sub will merge with and into Atkore, with Atkore surviving as a wholly owned subsidiary of Prysmian.

In connection with the Merger Agreement, the Guarantor has absolutely, unconditionally and irrevocably guaranteed the due and punctual payment and performance of the payment obligations of Prysmian and Merger Sub under the Merger Agreement.

As used in this section, the “Effective Time” means the time at which the certificate of merger with respect to the Merger is duly filed with the Secretary of State of the State of Delaware or at such later time as the parties may agree in writing and specify in such certificate of merger. At the Effective Time, the certificate of incorporation of

Merger Sub as in effect immediately prior to the Effective Time will be amended and restated as set forth in Exhibit A to the Merger Agreement and, as so amended and restated, will be the certificate of incorporation of the surviving corporation in the Merger, until thereafter amended. At the Effective Time, the bylaws of Merger Sub as in effect immediately prior to the Effective Time will be amended and restated as set forth in Exhibit B to the Merger Agreement and, as so amended and restated, will be the bylaws of the surviving corporation in the Merger, until thereafter amended. The directors of Merger Sub immediately prior to the Effective Time will be the initial directors of the surviving corporation in the Merger and the officers of Merger Sub immediately prior to the Effective Time will be the initial officers of the surviving corporation in the Merger, in each case effective as of the Effective Time and until their respective successors are duly elected or appointed and qualified or until their earlier death, resignation, incapacity or removal.

Unless another date, time or place is agreed to in writing by Atkore and Prysmian, the Closing will occur at 8:00 a.m. Eastern Time, remotely via electronic exchange of documents and signatures, no later than the fourth business day following the day on which the last of the conditions (other than those conditions that by their nature can only be satisfied on the closing date of the Merger, but subject to the satisfaction or waiver of such conditions) set forth in the Merger Agreement has been satisfied or waived.

The directors and officers of Merger Sub immediately prior to the Effective Time will be the initial directors and officers of the surviving corporation in the Merger as of the Effective Time, until their successors have been duly elected or appointed and qualified or until their earlier death, resignation, incapacity or removal, in accordance with the certificate of incorporation and bylaws of the surviving corporation and applicable law.

At the Effective Time, each share of Common Stock issued and outstanding immediately prior to the Effective Time (other than shares of Common Stock to be canceled or converted in accordance with the Merger Agreement or as to which appraisal rights have been properly exercised) will automatically be canceled and will cease to exist and each holder thereof will thereafter have no rights with respect to such securities except the right to receive the Merger Consideration of $95.00 per share of Common Stock in cash, without interest and subject to applicable withholding taxes. For more information, see “—Potential Adjustments to Merger Consideration.”

All shares of Common Stock owned directly by Prysmian, Atkore (including shares held as treasury stock or otherwise) or Merger Sub immediately prior to the Effective Time will be automatically canceled and will cease to exist, and no consideration will be delivered in exchange therefor. All shares of Common Stock owned by any wholly owned subsidiary of Prysmian (other than Merger Sub) or any wholly owned subsidiary of Atkore immediately prior to the Effective Time will be automatically converted into such number of shares of the surviving corporation so as to maintain relative ownership percentages.

Prysmian will make available to the paying agent the Merger Consideration to be paid in respect of certificates and book-entry shares formerly representing shares of Common Stock, as described below under “—Exchange of Atkore Stock Certificates and Book-Entry Shares.”

Prior to or at the Effective Time, Prysmian will enter into a customary paying agent agreement with a nationally recognized bank or trust company designated by Prysmian and reasonably acceptable to Atkore, which we refer to as the “paying agent.” Prior to or substantially concurrently with the Effective Time, Prysmian will deposit or cause to be deposited with the paying agent cash in an aggregate amount sufficient for the paying agent to pay the aggregate Merger Consideration payable in respect of shares of Common Stock in accordance with the Merger Agreement. The amount of Merger Consideration paid to holders of shares of Common Stock may be reduced by any applicable withholding taxes or other amounts required by applicable law to be withheld.

As soon as reasonably practicable following the Effective Time (and in any event not later than the fifth business day following the closing date of the Merger), the paying agent will send to each holder of record of a

stock certificate that formerly represented outstanding shares of Common Stock a letter of transmittal and instructions advising such stockholder how to surrender certificates in exchange for the Merger Consideration. Upon receipt of (1) surrendered certificates (or an appropriate affidavit for lost, stolen or destroyed certificates, together with any required bond) with respect to shares of Common Stock and (2) a signed letter of transmittal (in the case of Common Stock represented by stock certificates) and such other documents as may be required by the paying agent, the holder of such certificate will be entitled to receive the Merger Consideration, without interest and subject to applicable withholding taxes, and the surrendered certificates will be canceled. No interest will be paid or will accrue on any cash payable upon surrender of any certificates that formerly represented outstanding shares of Common Stock.

Any holder of book-entry shares of Common Stock will not be required to deliver a certificate or an executed letter of transmittal to the paying agent to receive the Merger Consideration to which such holder is entitled to receive in the Merger. Each holder of record of one or more book-entry shares converted into the Merger Consideration pursuant to the Merger Agreement will automatically upon the Effective Time be entitled to receive cash in an amount equal to the Merger Consideration multiplied by the number of shares of Common Stock previously represented by such book-entry shares, and the book-entry shares of such holder will be canceled. No interest will be paid or will accrue on any cash payable upon conversion of any book-entry shares that formerly represented outstanding shares of Common Stock.

If any cash deposited with the paying agent is not claimed within one year following the Effective Time, such cash will be delivered to the surviving corporation in the Merger, upon demand, and any former holder of shares of Common Stock who has not complied with the exchange procedures in the Merger Agreement will thereafter look only to the surviving corporation in the Merger for satisfaction of their claims for payment. None of Prysmian, Merger Sub, Atkore, the surviving corporation in the Merger or the paying agent will be liable to any person in respect of any cash amounts delivered to any public official pursuant to any applicable abandoned property law, escheat law or similar law.

Each of Prysmian, Atkore, the surviving corporation in the Merger and the paying agent (and any affiliates and designees of the foregoing and any other withholding agent) will be entitled to deduct and withhold from any amount otherwise payable to any person pursuant to the Merger Agreement such amounts as it is required to deduct and withhold with respect to the making of such payment under any provision of federal, state, local or foreign tax law. To the extent that amounts are so deducted or withheld and remitted to the applicable governmental body, agency, authority or entity, such deducted or withheld amounts will be treated for all purposes of the Merger Agreement as having been paid to the person in respect of whom such deduction and withholding was made.

If a certificate representing shares of Common Stock has been lost, stolen or destroyed, then, before an Atkore stockholder will be entitled to receive the Merger Consideration to be paid in respect of the shares of Common Stock represented by such lost, stolen or destroyed certificate, the holder will need to deliver an affidavit of that fact in form and substance reasonably acceptable to Prysmian, and, if required by Prysmian or the paying agent, post a bond in a reasonable and customary amount as Prysmian or the paying agent may direct, as indemnity against any claim that may be made against it or the surviving corporation in the Merger with respect to such certificate.

In the event that, before the completion of the Merger, any change in the number or class of outstanding shares of Common Stock occurs as a result of any reclassification, stock split (including a reverse stock split), recapitalization, split-up, combination, exchange of shares, readjustment or other similar transaction, or any stock dividend is declared thereon with a record date during such period, the Merger Consideration and any other similarly dependent item, as the case may be, will be appropriately adjusted in order to provide Prysmian the same economic effect as contemplated by the Merger Agreement prior to such event.

Pursuant to the Merger Agreement, each Company Option that is outstanding immediately prior to the Effective Time, whether or not vested, will be deemed fully vested and canceled and converted into the right to receive a cash

payment from the surviving corporation in the Merger equal to the product obtained by multiplying (A) the excess, if any, of the Merger Consideration over the exercise price per share of such Company Option by (B) the total number of shares of Common Stock underlying such Company Option.

At the Effective Time, each Company Option with an exercise price per share that is equal to or greater than the Merger Consideration will be canceled for no consideration.

At the Effective Time, each Company RSU that is outstanding immediately prior to the Effective Time, whether or not vested, will be deemed fully vested and canceled and converted into the right to receive a cash payment from the surviving corporation in the Merger equal to the product of (A) the Merger Consideration and (B) the total number of shares of Common Stock underlying such Company RSU. Any Company RSUs granted to an Atkore employee after August 2, 2026, if any and to the extent outstanding and unvested immediately prior to the Effective Time, will be converted into the contingent right to receive an amount in cash, without interest, equal to the product of (A) the Merger Consideration and (B) the total number of shares of Common Stock underlying such Company RSU, with such contingent right remaining subject to the same terms and conditions (including vesting schedule and pro rata vesting upon a qualifying termination of employment), that applied to such Company RSU immediately prior to the Effective Time.

At the Effective Time, each Company PSU that is outstanding immediately prior to the Effective Time, whether or not vested, will be canceled and converted into the right to receive a cash payment from the surviving corporation equal to the product of (A) the Merger Consideration and (B) the total number of shares of Common Stock underlying such Company PSU. The number of shares of Common Stock underlying a Company PSU will be determined in accordance with the applicable terms of such Company PSU.

At the Effective Time, each Company DSU that is outstanding immediately prior to the Effective Time, whether or not vested, will be deemed fully vested and canceled and converted into the right to receive a cash payment from the surviving corporation equal to the product of (A) the Merger Consideration and (B) the total number of shares of Common Stock underlying such Company DSU.

For additional information on Atkore’s equity awards, including the interests of Atkore’s directors and executive officers in the Merger and the Merger-related compensation which may be payable to Atkore’s named executive officers, see “The Merger—Interests of Atkore’s Directors and Executive Officers in the Merger” and “The Merger—Quantification of Potential Payments and Benefits to Atkore’s Named Executive Officers in Connection with the Merger,” respectively.

The Merger Agreement provides that, subject to certain exceptions or unless Prysmian approves in writing in advance (such approval not to be unreasonably withheld, conditioned or delayed), between August 2, 2026 and the Effective Time, Atkore will use its commercially reasonable efforts to conduct the business of Atkore and its subsidiaries in all material respects in the ordinary course of business consistent with past practice and to the extent consistent therewith, use its commercially reasonable efforts to preserve intact, in all material respects, Atkore and its subsidiaries’ business organizations, material assets and properties and maintain Atkore and its subsidiaries’ existing material business relationships and goodwill.

In addition, Atkore has agreed that during this period, subject to certain exceptions or unless Prysmian approves in writing (such approval not to be unreasonably withheld, conditioned or delayed), it will not, and will cause its subsidiaries not to:

The Merger Agreement requires Atkore, as promptly as practicable after the date of the Merger Agreement (and in any event within 20 business days), to prepare and file with the SEC this proxy statement. Atkore will cause this

proxy statement to be mailed to Atkore stockholders as of the Record Date no later than three business days following the date on which this proxy statement is cleared by the SEC. Atkore will duly call, give notice of, convene and hold the Special Meeting as promptly as reasonably practicable following the clearance of this proxy statement, and in any event within 35 days thereafter.

Without the prior written consent of Prysmian, matters contemplated by this proxy statement are the only matters (other than matters of procedure and matters required by applicable law to be voted on by Atkore stockholders in connection therewith and the transactions contemplated by the Merger Agreement) that Atkore may propose to be voted on by Atkore stockholders at the Special Meeting. Atkore will not schedule any other meeting of its stockholders prior to the Special Meeting, other than Atkore’s annual meeting of stockholders held consistent with past practice so long as only matters typically presented at Atkore’s annual meetings of stockholders, including any stockholder proposals received in the ordinary course that are (i) not related to the Merger or the transactions contemplated by the Merger Agreement and (ii) required under applicable law as determined in good faith by Atkore, are presented at such meeting.

Atkore may not adjourn, postpone or otherwise delay the Special Meeting without the prior written consent of Prysmian (such consent not to be unreasonably withheld, conditioned or delayed) unless (i) Atkore believes in good faith that such adjournment or postponement is reasonably necessary to allow reasonable additional time to (x) solicit additional proxies necessary to obtain stockholder approval of the Merger Proposal or (y) distribute any supplement or amendment to this proxy statement, the distribution of which the Board has determined in good faith to be necessary under applicable law, or (ii) for an absence of a quorum, in which case Atkore will use its reasonable best efforts to obtain a quorum as promptly as practicable.

Notwithstanding the foregoing, Atkore may not, without the prior written consent of Prysmian (such consent not to be unreasonably withheld, conditioned or delayed), adjourn or postpone the meeting of its stockholders more than a total of three times pursuant to clauses (i)(x) or (ii) of the immediately preceding paragraph, and no such adjournment or postponement will be, without the prior written consent of Prysmian (such consent not to be unreasonably withheld, conditioned or delayed), for a period exceeding 10 business days in connection with any one adjournment or postponement or more than an aggregate of 30 days.

If Atkore provides a Company Superior Proposal Notice or Intervening Event Notice (each as defined in the Merger Agreement) to Prysmian on a date that is less than five business days before the Special Meeting, Atkore will, if requested by Prysmian acting reasonably, postpone the Special Meeting to a date determined by Prysmian that is not more than 10 business days after the scheduled date of the Special Meeting (but in any event the Special Meeting will not be postponed to a date which would prevent the Effective Time from occurring on or prior to the End Date (as defined below)).

Atkore will otherwise coordinate and cooperate with Prysmian with respect to the timing of the Special Meeting, including consulting with Prysmian regarding the Record Date prior to setting such date. Atkore will provide updates to Prysmian with respect to the proxy solicitation for the Special Meeting (including interim results) as reasonably requested by Prysmian.

Atkore has agreed that it and its subsidiaries will not, and that it will direct and use its reasonable best efforts to cause its and its subsidiaries’ respective representatives not to, directly or indirectly:

Nothing contained in the Merger Agreement will prevent the Board from making any disclosure if, in the good faith judgment of the Board, after consultation with outside counsel, the failure to make such disclosure would be reasonably likely to be inconsistent with the Board members’ exercise of their fiduciary duties to Atkore’s stockholders under applicable law. Additionally, Atkore may make any “stop, look and listen” communication to Atkore stockholders pursuant to Rule 14d-9(f) under the Exchange Act (and no communication that consists solely of a “stop, look and listen” statement, in and of itself, will be considered a Change in the Board Recommendation) and comply with disclosure obligations under Rule 14e-2(a), Rule 14d-9 or Item 1012(a) of Regulation M-A promulgated under the Exchange Act or the rules and regulations of the NYSE with regard to an Acquisition Proposal; provided that no disclosure or communication will be permitted that constitutes a Change in the Board Recommendation or that requires the giving of a Company Superior Proposal Notice or Intervening Event Notice, except in accordance with the Merger Agreement.

In addition, but subject to the terms and conditions contained in the Merger Agreement, prior to obtaining the stockholder approval, Atkore may, directly or indirectly through its advisors, agents or other intermediaries:

Atkore may only furnish information and participate in discussions as described above, however, if and only if (i) Atkore first delivers to Prysmian written notice advising Prysmian that Atkore intends to take such action, and (ii) prior to furnishing any such information or affording any such access, Atkore receives from the person making the Acquisition Proposal an executed confidentiality agreement having provisions that are not materially less favorable in any substantive respect to Atkore than the provisions of the existing confidentiality agreement between Atkore and Prysmian; provided that such confidentiality agreement need not contain any “standstill” or similar provisions.

Atkore also agrees that any material nonpublic information provided to such person described in the immediately preceding bullet that has not previously been provided to Prysmian will be provided to Prysmian prior to or substantially concurrently with the time it is provided to such person.

In the event that, after the date of the Merger Agreement, Atkore receives an Acquisition Proposal, or any proposal, offer, inquiry or request (including any request for nonpublic information relating to Atkore or any of its subsidiaries or for access to the properties, books, or records of Atkore or any of its subsidiaries) that constitutes or would reasonably be expected to result in or lead to any Acquisition Proposal, Atkore will:

A “Company Superior Proposal” is a bona fide written Acquisition Proposal made after the date of the Merger Agreement not resulting from a material breach of the non-solicitation provisions of the Merger Agreement that would result in a person or group of persons (or their stockholders) becoming, directly or indirectly, the beneficial owner of 50% or more of Atkore’s consolidated total assets, Atkore’s consolidated total assets to which 50% or more of the revenues or earnings of Atkore and its subsidiaries are attributable for the most recent fiscal year for which the audited financial statements are then available, or 50% or more of the total voting power of the equity securities of Atkore (or any direct or indirect parent company thereof or successor company thereto), that the Board has determined in its good faith judgment, after consultation with its outside legal and financial advisors, taking into account all the terms and conditions of such Acquisition Proposal, including likelihood of consummation on the terms proposed and all legal, financial and regulatory aspects of such proposal, as well as any revisions to the terms of the transactions contemplated by the Merger Agreement offered in writing by Prysmian pursuant to the matching rights provisions, is more favorable to Atkore’s stockholders from a financial point of view than the transactions contemplated by the Merger Agreement and has a reasonable likelihood of being completed on the terms proposed.

Atkore has agreed that the Board will recommend the adoption of the Merger Agreement to Atkore stockholders (the “Board Recommendation”). The Merger Agreement provides that, subject to the exceptions described below, neither the Board nor any committee thereof will (i) withdraw, modify or qualify, or propose publicly to withdraw, modify or qualify, in any manner adverse to Prysmian, the approval of the Merger Agreement, the Merger or the Board Recommendation, (ii) approve, recommend, adopt, authorize, or declare advisable, or propose publicly to approve, recommend, adopt, authorize or declare advisable, any Acquisition Proposal, (iii) fail to publish, send or provide to the holders of Common Stock, pursuant to Rule 14e-2(a) under the Exchange Act, a statement recommending against any Acquisition Proposal that is a tender or exchange offer and publicly reaffirming the Board Recommendation within 10 business days after the commencement (within the meaning of Rule 14d-2 under the Exchange Act) of such tender offer or exchange offer, (iv) if an Acquisition Proposal (other than an Acquisition Proposal that is a tender or exchange offer) or any material modification thereof has been publicly announced or disclosed, fail to recommend against such Acquisition Proposal or material modification thereof or fail to reaffirm the Board Recommendation within 10 business days after Prysmian so requests in writing following such public announcement or disclosure (or, if earlier, at least two business days prior to the Special Meeting), or (v) publicly announce an intention to effect any of the foregoing (any of the foregoing, a “Change in the Board Recommendation”). For purposes of the Merger Agreement, a Change in the Board Recommendation includes any failure by Atkore to include the Board Recommendation in this proxy statement. Notwithstanding the foregoing restrictions, prior to obtaining the stockholder approval, the Board is permitted to make or change its recommendation in response to a Company Superior Proposal or Intervening Event (as defined below) as discussed below.

The Board is permitted, in response to an Acquisition Proposal received after the date of the Merger Agreement, which has not been subsequently withdrawn and did not result from a breach of the non-solicitation provisions of the Merger Agreement, to effect a Change in the Board Recommendation, or to cause Atkore to terminate the Merger Agreement in accordance with its terms to enter into a definitive agreement providing for a Company Superior Proposal (so long as, prior to or concurrently with such termination, Atkore pays to Prysmian the Company Termination Fee of $115,920,000), if and only if:

The Board is permitted, in response to an Intervening Event, to effect a Change in the Board Recommendation, if:

An “Intervening Event” means any Effect (as defined below) that is (i) material to Atkore, (ii) was unknown to, and not reasonably foreseeable by, the Board as of the date of the Merger Agreement, or if known and reasonably

foreseeable to the Board as of the date of the Merger Agreement, the material consequences of which were not known or reasonably foreseeable to the Board as of the date of the Merger Agreement, and (iii) does not involve or relate to (A) an Acquisition Proposal, or (B) (x) any failure by Atkore and its subsidiaries to meet any internal or public projections or forecasts or estimates of revenues or earnings for any period, or (y) any change in the price or trading volume of Common Stock or the credit rating or other rating of financial strength of Atkore, its subsidiaries or any of their respective securities (provided, that, for purposes of clause (B), the matters giving rise to or contributing to such events may be deemed to constitute, or be taken into account in determining whether there has been, an Intervening Event, to the extent not otherwise excluded by the definition of Intervening Event).

However, even if the Board effects a Change in the Board Recommendation, Atkore must still call a stockholder meeting as otherwise required by the Merger Agreement and submit the Merger Agreement and the Merger to the vote of Atkore’s stockholders (unless Atkore terminates the Merger Agreement in order to accept a Company Superior Proposal).

Atkore and Prysmian have agreed to use their reasonable best efforts to take, or cause to be taken, all actions, and to do, or cause to be done, all things necessary, proper or advisable under applicable laws to consummate and make effective the Merger and the other transactions contemplated by the Merger Agreement as promptly as practicable after the date of the Merger Agreement and, in any event, prior to the End Date, including:

Prior to Closing, Atkore and Prysmian have agreed to each keep the other apprised of the status of certain matters relating to the completion of the Merger and work cooperatively in connection with obtaining all required approvals or consents of any governmental entity in connection with the Merger as specified in the Merger Agreement. Except as prohibited by applicable law or governmental order, Atkore and Prysmian will (i) cooperate and consult with each other in connection with any filing or submission with a governmental entity in connection with the transactions contemplated by the Merger Agreement and in connection with any investigation or inquiry by or before a governmental entity relating to the transactions contemplated by the Merger Agreement, including any proceeding initiated by a private party, including by allowing the other party to have a reasonable opportunity to review in advance and comment on drafts of filings and submissions, (ii) promptly inform the other party of any substantive communication received from, or given to, the FTC, the Antitrust Division or any other governmental entity and of any substantive communication received from, or given in connection with any proceeding by a private party, in each case regarding any of the transactions contemplated by the Merger Agreement, (iii) consult with each other prior to taking any material position in discussions with or filings to be submitted to any governmental entity, (iv) permit the other party to review and discuss in advance, and consider in good faith the views of the other in connection with, any analyses, presentations, memoranda, briefs, arguments, opinions and proposals to be submitted to any governmental entity and (v) coordinate with the other party in preparing and exchanging such information and promptly provide the other (and its counsel) with copies of all filings, presentations or submissions (and a summary of any oral presentations) made by such party with any governmental entity relating to the Merger Agreement or the transactions contemplated thereby; provided that each party is permitted to redact any materials (A) to remove references concerning the valuation of Atkore, (B) as necessary to comply with contractual arrangements or applicable law and (C) as necessary to address reasonable attorney-client or other privileged, confidentiality or competitively sensitive information concerns. Unless prohibited by applicable law or governmental order, none of Atkore, Prysmian or their respective affiliates will participate in or attend any meeting, or engage in any substantive conversation, with any governmental entity in respect of the transactions contemplated

by the Merger Agreement without giving the other party the opportunity to attend and participate. In the event of any dispute between the parties relating to strategy in connection with obtaining any necessary approvals under antitrust laws or foreign investment laws with respect to the Merger and the other transactions contemplated by the Merger Agreement, the parties will escalate such dispute to the chief legal officers of Atkore and Prysmian for resolution; provided, that, if any such dispute remains unresolved, Prysmian will have the right to make the final determination with respect to such matter acting reasonably and in good faith and in a manner consistent with Prysmian’s regulatory efforts obligations under the Merger Agreement.

Without limiting the foregoing, Prysmian and its affiliates have also agreed to use reasonable best efforts to take all actions necessary to avoid or eliminate each and every impediment that may be asserted by any governmental entity with respect to the transactions contemplated by the Merger Agreement so as to enable the Closing to occur as promptly as practicable and, in any event, prior to the End Date, including:

However, notwithstanding the foregoing, Prysmian and its affiliates are not required to (x) proffer or agree to any Remedial Action with respect to assets, rights, product lines, categories of assets or businesses or other operations or interests therein of Prysmian or any of its pre-Closing affiliates, or (y) proffer or agree to any Remedial Action with respect to specified assets of Atkore or its subsidiaries identified in the Merger Agreement. Atkore and its subsidiaries are not permitted to proffer or agree to any Remedial Action without the prior written consent of Prysmian, and, if requested by Prysmian in writing, Atkore will agree to any Remedial Action; provided that Atkore is not required to (1) agree to any Remedial Action that is not conditioned on the consummation of the Closing or (2) pay, prior to the Effective Time, any fee, penalty or other consideration to any third party for any consent or approval required for or triggered by the consummation of the transactions contemplated by the Merger Agreement under any contract or agreement or otherwise.

Prysmian has also agreed not to, and to cause its affiliates not to, acquire or agree to acquire by merging or consolidating with, or by purchasing a substantial portion of the assets of or equity in, or by any other manner, any person or portion thereof, or otherwise acquire or agree to acquire any assets, or commence any new business, if any such action would reasonably be expected to materially delay the obtaining of, or materially increase the risk of not obtaining, any

consent, approval, authorization, declaration, waiver, license, franchise, permit, certificate or order of any governmental entity necessary to consummate the transactions contemplated by the Merger Agreement or prevent, materially delay or materially impede the consummation of the transactions contemplated by the Merger Agreement.

For a period of 12 months following the Effective Time, the surviving corporation in the Merger and its subsidiaries will (and Prysmian will cause the surviving corporation in the Merger and its subsidiaries to) provide each individual who is employed by Atkore or any of its subsidiaries as of the Effective Time and continues to be employed with Prysmian or any of its subsidiaries as of immediately following the Effective Time (a “Continuing Employee”) with:

During such 12-month period (or such longer period required by the terms of the applicable Company Plan), the surviving corporation in the Merger and its subsidiaries will (and Prysmian will cause the surviving corporation in the Merger and its subsidiaries to) provide each Continuing Employee with severance and termination benefits that are no less favorable than those applicable to such Continuing Employee immediately before the Effective Time and as disclosed by Atkore to Prysmian prior to the date of the Merger Agreement.

With respect to each benefit or compensation plan, program, policy, arrangement or agreement that is made available to any Continuing Employee at or after the Effective Time (each such plan, a “New Plan”), the surviving corporation in the Merger and its subsidiaries will (and Prysmian will cause the surviving corporation in the Merger and its subsidiaries to) use commercially reasonable efforts to grant to such Continuing Employee credit for all service with Atkore prior to the Effective Time for purposes of eligibility to participate, vesting and entitlement to benefits where length of service is relevant (including for purposes of vacation accrual, severance entitlement or termination pay), subject to certain exceptions.

In addition, (i) the surviving corporation in the Merger and its subsidiaries will use commercially reasonable efforts to cause each Continuing Employee to be immediately eligible to participate, without any waiting period, in any and all New Plans to the extent that coverage pursuant to any New Plan replaces coverage pursuant to a corresponding Company Plan (such plans, the “Old Plans”), (ii) for purposes of each New Plan providing life insurance, medical, dental, pharmaceutical, vision or disability benefits, the surviving corporation in the Merger and its subsidiaries will use commercially reasonable efforts to cause all waiting periods, pre-existing condition exclusions, evidence of insurability requirements and actively-at-work or similar requirements of such New Plan to be waived for the Continuing Employees and their covered dependents and (iii) for purposes of each New Plan providing medical, dental, pharmaceutical, or vision benefits, the surviving corporation in the Merger and its subsidiaries will use commercially reasonable efforts to cause any eligible expenses incurred by the Continuing Employees and their covered dependents during the portion of the plan year of the Old Plans ending on the date that Continuing Employees’ participation in the corresponding New Plan begins to be given full credit pursuant to such New Plan for purposes of satisfying all deductible, coinsurance and maximum out-of-pocket requirements applicable to such Continuing Employees and their covered dependents for the applicable plan year as if such amounts had been paid in accordance with such New Plan. Any vacation or paid time off accrued but unused by a Continuing Employee as of immediately prior to the Effective Time will be credited to such Continuing Employee following the Effective Time and will not be subject to accrual limits or other forfeiture and will not limit future accruals.

With respect to each Continuing Employee’s annual bonus for the fiscal year in which the Closing occurs (the “Closing Year Annual Bonus”), Prysmian will, or will cause the surviving corporation in the Merger to, pay to each Continuing Employee a pro rata portion of the Closing Year Annual Bonus in an amount determined assuming (i) with respect to individual performance goals, that such goals are achieved at no less than target levels of performance and

(ii) with respect to company performance goals, that such goals are achieved at the greater of (x) target performance and (y) actual performance as of the closing date of the Merger (as determined by Atkore in good faith immediately prior to the Closing), and pro-rated by a fraction, the numerator of which is the number of days elapsed in the fiscal year of Closing prior to the Closing and the denominator of which is 365 (the “Pro Rata Bonus Payment”). The Pro Rata Bonus Payment will be payable at the same time and subject to the same terms and conditions as called for in the applicable bonus plan in effect at the Effective Time, unless the Continuing Employee’s employment is terminated prior to the applicable payment date for the Closing Year Annual Bonus by the surviving corporation in the Merger without “cause,” in which case, if the Continuing Employee executes and does not revoke a customary general release, the Continuing Employee will be entitled to receive an amount in cash no less than the Pro Rata Bonus Payment no later than sixty (60) days following such termination. If any Continuing Employees participating in the Executive Severance Policy experience a termination without “cause” prior to the applicable payment date, they will not be eligible for Pro Rata Bonus Payment and will instead receive the pro-rated annual bonus provided in the Executive Severance Policy.

From and after the Effective Time, the surviving corporation in the Merger will (and Prysmian will cause the surviving corporation in the Merger to) (i) assume and honor all of the Company Plans in accordance with their terms as in effect immediately prior to the Effective Time and, in good faith, interpret the provisions of such Company Plans consistent with past practice and no less favorably than the manner in which they have been interpreted in the past and (ii) assume all collective bargaining agreements to which Atkore or any of its subsidiaries is a party in accordance with their terms as in effect immediately prior to the Effective Time.

For additional information on certain other compensation-related matters covered in the Merger Agreement that affect Atkore’s directors and executive officers, see the section titled “The Merger—Interests of Atkore’s Directors and Executive Officers in the Merger” and “The Merger—Quantification of Potential Payments and Benefits to Atkore’s Named Executive Officers in Connection with the Merger.”

Prysmian has agreed that:

Atkore has agreed that, prior to the earlier of the Closing or termination of the Merger Agreement, Atkore will, and will cause its subsidiaries to, and will use commercially reasonable efforts to cause its representatives to use their reasonable best efforts to provide customary cooperation reasonably requested by Prysmian or Merger Sub, at Prysmian’s sole cost and expense, in connection with Prysmian’s efforts to obtain any debt financing in connection with the transactions contemplated by the Merger Agreement (the “Financing”), including:

Such cooperation will not require Atkore, its subsidiaries or their respective representatives to, among other things, (i) take any action that would (or would reasonably be expected to) cause the failure of any closing condition

or any condition related to the availability of the Financing at the Closing, or cause Atkore to breach any representation, warranty, covenant or agreement in the Merger Agreement, (ii) enter into or otherwise approve or perform any agreement, commitment, document, certificate or instrument (or a modification thereof) effective prior to the Closing, (iii) deliver legal opinions, reliance letters, solvency certificates or other certificates, or adopt resolutions or take other corporate action, effective prior to the Closing, (iv) pay any commitment or other similar fee or incur any liability or give any indemnities in connection with the Financing prior to the Closing (other than payments subject to reimbursement by Prysmian), (v) provide information the disclosure of which is prohibited or restricted by law or would result in the loss or waiver of any privilege or similar protections, (vi) take any action that would unreasonably disrupt Atkore’s business operations, conflict with applicable laws or result in a breach or default under its material contracts or organizational documents, or (vii) provide any projections, estimates or pro forma financial information relating to the transactions (which will be the sole responsibility of Prysmian and Merger Sub).

Prysmian will reimburse Atkore for all reasonable and documented out-of-pocket expenses incurred in connection with such financing cooperation and will indemnify Atkore, its subsidiaries and their respective representatives from and against any losses suffered or incurred in connection with such cooperation, the Financing, the credit facility terminations and the redemption of Atkore’s senior notes, subject to certain exceptions for fraud, willful misconduct, gross negligence or material misstatements or omissions in information provided by Atkore.

The obtaining of the Financing is not a condition to Closing. A breach of the financing cooperation provisions will not constitute a breach by Atkore for purposes of Prysmian’s closing conditions unless (i) Prysmian has provided written notice of such breach and Atkore has failed to cure, (ii) such breach is a Willful Breach (as defined in the Merger Agreement) and (iii) such breach is the primary cause of the Financing not being consummated.

The Merger Agreement contains certain other covenants and agreements, including covenants relating to, among other matters:

Atkore makes various representations and warranties to Prysmian in the Merger Agreement that are subject in some cases to exceptions and qualifications set forth in the Merger Agreement. These representations and warranties relate to, among other things:

In addition, Prysmian and Merger Sub make representations and warranties to Atkore that are subject in some cases to exceptions and qualifications set forth in the Merger Agreement. These representations and warranties relate to, among other things:

The representations and warranties in the Merger Agreement generally do not survive the Effective Time or any termination of the Merger Agreement.

Certain of the representations and warranties made by the parties are qualified as to “knowledge,” “materiality,” or, as applicable, “Company Material Adverse Effect.” For purposes of the Merger Agreement, “Company Material Adverse Effect” means any effect, event, development, change, state of facts, condition, circumstance or occurrence (each, an “Effect”) that, individually or in the aggregate with any other Effect, is, or would reasonably be expected to be, materially adverse to the condition (financial or otherwise), properties, assets, operations, liabilities, business or results of operations of Atkore and its subsidiaries, taken as a whole. However, none of the following, alone or in combination, will be deemed to constitute a Company Material Adverse Effect, or be taken into account in determining whether a Company Material Adverse Effect has occurred or would reasonably be expected to occur:

The obligations of each of Atkore, Prysmian and Merger Sub to complete the Merger are subject to the satisfaction or waiver of the following conditions:

In addition, the obligations of Atkore to complete the Merger are subject to the satisfaction or, to the extent permitted by law and in accordance with the Merger Agreement, waiver of the following conditions:

In addition, the obligations of Prysmian and Merger Sub to complete the Merger are subject to the satisfaction or, to the extent permitted by law and in accordance with the Merger Agreement, waiver of the following conditions:

The Merger Agreement may be terminated at any time prior to the Effective Time, even if Atkore’s stockholders have previously approved the Merger, in any of the following ways:

If the Merger Agreement is terminated as described above, the terminating party will forthwith give written notice thereof to the other party or parties and the Merger Agreement will terminate, and the transactions contemplated thereby will be abandoned, without further action by any of the parties. Upon a valid termination, the Merger Agreement will become void and have no effect, and there will be no liability or obligation on the part of any party, except that:

Atkore has agreed to pay or cause to be paid to Prysmian the Company Termination Fee, equal to $115,920,000, in connection with a termination of the Merger Agreement under the following circumstances:

Except as described above, all costs and expenses (including fees and expenses of counsel and financial advisors) incurred in connection with the Merger Agreement will be paid by the party incurring such costs or expenses, except that Prysmian will pay all filing fees payable under the HSR Act or in connection with any other applicable antitrust laws or foreign investment laws, regardless of whether the transactions contemplated by the Merger Agreement are consummated.

Subject to applicable law and unless stated otherwise in the Merger Agreement, any provision of the Merger Agreement may be amended, modified or waived prior to the Effective Time if the amendment, modification or waiver is in writing and signed, in the case of an amendment or modification, by each party (and Guarantor, if the amendment is to certain provisions of the Merger Agreement) or, in the case of a waiver, by the party against whom the waiver is to be effective. The conditions to each of the parties’ respective obligations to consummate the transactions contemplated by the Merger Agreement are for the sole benefit of such party and may be waived by such party in whole or in part to the extent permitted by applicable law.

The Merger Agreement is to be construed in accordance with and governed by the law of the State of Delaware, without regard to principles of conflicts of laws. Each of the parties agrees that: (i) it will bring any proceeding in connection with, arising out of or otherwise relating to the Merger Agreement, any instrument or other document delivered pursuant to the Merger Agreement or the transactions contemplated thereby exclusively in the Court of Chancery of the State of Delaware, or (and only if) such court finds it lacks subject matter jurisdiction, the Superior Court of the State of Delaware (Complex Commercial Division); provided that if subject matter jurisdiction over the matter that is the subject of the proceeding is vested exclusively in the United States federal courts, such proceeding will be heard in the United States District Court for the District of Delaware (the courts in this clause (i), together with any appellate court thereof, the “Chosen Courts”); and (ii) solely in connection with such proceedings, (A) it irrevocably and unconditionally submits to the exclusive jurisdiction of the Chosen Courts, (B) it waives any objection to the laying of venue in any proceeding in the Chosen Courts, (C) it waives any objection that the Chosen Courts are an inconvenient forum or do not have jurisdiction over any party, (D) mailing of process or other papers in connection with any such proceeding in the manner provided in the Merger Agreement or in such other manner as may be permitted by applicable law will be valid and sufficient service thereof and (E) it will not assert as a defense, any matter or claim waived by the foregoing clauses (A) through (D) or that any governmental order issued by the Chosen Courts may not be enforced in or by the Chosen Courts.

Each of the parties to the Merger Agreement irrevocably waives any and all right to trial by jury in any legal proceeding arising out of or related to the Merger Agreement or the transactions contemplated thereby.

The parties will be entitled to enforce specifically the terms and provisions of the Merger Agreement and to obtain an injunction restraining any breach or violation or threatened breach or violation of the provisions of the

Merger Agreement, in addition to any other available remedies at equity or at law, without necessity of posting a bond or other form of security. In the event that any proceeding is brought in equity to enforce the provisions of the Merger Agreement, no party will allege, and each party waives the defense, that there is an adequate remedy at law.

The Merger Agreement is not intended to, and does not, confer upon any person other than the parties and their respective successors, legal representatives and permitted assigns any rights or remedies, express or implied, except:

Guarantor has absolutely, unconditionally and irrevocably guaranteed, as primary obligor and not as surety, the due and punctual payment and performance of the payment obligations of Prysmian and Merger Sub under the Merger Agreement (the “Guaranteed Obligations”). The guaranty is an absolute, unconditional and continuing guaranty of the full and punctual discharge and performance of the Guaranteed Obligations and is a guaranty of payment and performance, not of collection.

If Prysmian or Merger Sub defaults in the payment of any of the Guaranteed Obligations, the Guarantor will, as soon as reasonably practicable following demand, unconditionally perform and satisfy the Guaranteed Obligations in the manner prescribed by the Merger Agreement. The Guaranteed Obligations will be discharged upon (i) indefeasible payment in full in accordance with the Merger Agreement, or (ii) those defenses to payment that Prysmian or Merger Sub has arising from Fraud or Willful Breach by Atkore or under the specific terms of the Merger Agreement.

The Guarantor has represented and warranted that it is duly organized, validly existing and in good standing, has all requisite corporate power and authority to enter into the guaranty, and that the guaranty has been duly authorized, executed and delivered and constitutes a valid and binding obligation of the Guarantor.

For so long as the guaranty remains in effect, the Guarantor will not consolidate with or merge into any other person, or transfer all or substantially all of its assets to any person, unless the resulting, surviving or transferee person expressly assumes all of the Guarantor’s obligations under the guaranty, and the Guarantor will not take any action outside the ordinary course of business that would reasonably be expected to render it unable to perform its obligations thereunder. In no event will the potential liability of the Guarantor in connection with the Merger Agreement or the transactions contemplated thereby exceed that of Prysmian.

The Merger Agreement provides that the financing parties with respect to the Financing are express third-party beneficiaries of certain provisions of the Merger Agreement, that any legal action involving the financing parties arising out of or relating to the Merger Agreement or the Financing will be subject to the exclusive jurisdiction of the courts in the Borough of Manhattan, New York, governed by New York law, subject to certain exceptions set forth in the Merger Agreement, and that the financing parties will not have any liability to Atkore or its subsidiaries or their respective controlled affiliates or representatives relating to or arising out of the Merger Agreement or the Financing. These limitations do not affect Prysmian’s obligations under the Merger Agreement or Atkore’s rights against the financing parties following the closing date of the Merger.

The discussion of the provisions set forth below is not a complete summary regarding your appraisal rights under Delaware law and is qualified in its entirety by reference to Section 262 of the DGCL, which may be accessed without subscription or cost at https://delcode.delaware.gov/title8/c001/sc09/index.html#262 and is incorporated by reference herein. Holders of record and beneficial owners of shares of Common Stock intending to exercise appraisal rights should carefully review Section 262 of the DGCL in its entirety and the information set forth below. Failure to follow precisely any of the statutory procedures set forth in Section 262 of the DGCL in a timely manner will result in a loss of appraisal rights. This summary does not constitute any legal or other advice, nor does it constitute a recommendation that you exercise your appraisal rights under Section 262 of the DGCL.

All references in Section 262 of the DGCL and this summary to “stockholder” are to the record holder of the shares of Common Stock; all references to “beneficial owner” are to a person who is the beneficial owner of shares of Common Stock held either in voting trust or by a nominee on behalf of such person; and all references to “person” are to any individual, corporation, partnership, unincorporated association or other entity. Failure to comply strictly with the procedures set forth in Section 262 of the DGCL will result in a loss of appraisal rights.

Holders of record and beneficial owners of shares of Common Stock have the right under Section 262 of the DGCL to seek appraisal of the “fair value” of their shares of Common Stock, as determined in accordance with Delaware law. A holder of record or beneficial owner of shares of Common Stock must satisfy the requirements of Section 262 of the DGCL to exercise and perfect appraisal rights and follow precisely the statutory procedures pursuant to Section 262 of the DGCL in a timely manner.

Under Section 262 of the DGCL, if the Merger is completed and certain conditions under Section 262(g) of the DGCL are satisfied, holders of record and beneficial owners of shares of Common Stock who (i) have delivered a written demand for appraisal of such holder’s or owner’s shares of Common Stock in compliance with Section 262 of the DGCL to Atkore prior to the vote on the Merger Proposal, (ii) do not vote, in person or by proxy, in favor of the Merger Proposal, (iii) continuously hold of record or beneficially own such shares on the date of making the demand for appraisal through the Effective Time, and (iv) otherwise comply with the statutory requirements set forth in Section 262 of the DGCL are entitled to have their shares of Common Stock appraised by the Delaware Court of Chancery and to receive payment in cash, in lieu of the Merger Consideration, for the “fair value” of their shares of Common Stock, exclusive of any element of value arising from the accomplishment or expectation of the Merger, together with (unless the Delaware Court of Chancery in its discretion determines otherwise for good cause shown) interest, if any, on the amount determined by the Delaware Court of Chancery to be the “fair value.” The “fair value” of such shares of Common Stock, as determined by the Delaware Court of Chancery may be less than, equal to or more than the Merger Consideration.

Under Section 262 of the DGCL, where the proposed merger for which appraisal rights are provided is to be submitted for approval at a meeting of Atkore’s stockholders, Atkore is required, not less than 20 days before the Special Meeting, to notify each stockholder as of the Record Date who is entitled to appraisal rights that appraisal rights are available for any or all of the shares of Common Stock, and must include in the required notice either a copy of Section 262 of the DGCL or information directing the stockholders to a publicly available electronic resource at which Section 262 of the DGCL may be accessed without subscription or cost. This proxy statement constitutes such notice to stockholders, and Section 262 of the DGCL may be accessed without subscription or cost at https://delcode.delaware.gov/title8/c001/sc09/index.html#262. Any holder of record or beneficial owner of shares of Common Stock who wishes to exercise their appraisal rights or who wishes to preserve their right to do so should review Section 262 of the DGCL carefully, because failure to timely and properly comply with the procedures specified therein will result in the loss of appraisal rights under the DGCL. A stockholder or beneficial owner who loses such holder’s or owner’s appraisal rights will be entitled to receive the Merger Consideration without interest and less any applicable withholding taxes. Because of the complexity of Section 262 of the DGCL, any holder of record or beneficial owner of shares of Common Stock who desires to exercise their appraisal rights should consult their legal and financial advisors.

Holders of record and beneficial owners of shares of Common Stock who desire to exercise their appraisal rights must deliver to Atkore a written demand for appraisal of their shares of Common Stock no later than before the taking of the vote on the Merger Proposal at the Special Meeting, which is scheduled to occur on    , 2026. In the case of a written demand for appraisal made by a stockholder, a demand for appraisal will be sufficient if it reasonably informs Atkore of the identity of the stockholder and that such stockholder intends thereby to demand appraisal of such stockholder’s shares of Common Stock. In the case of a written demand for appraisal made by a

beneficial owner, the demand must reasonably identify the record holder of the shares for which the demand is made, be accompanied by documentary evidence of such beneficial owner’s beneficial ownership of such stock and a statement that such documentary evidence is a true and correct copy of what it purports to be and provide an address at which such beneficial owner consents to receive notices given by the surviving corporation in the Merger and to be set forth on the verified list (as defined below).

In addition, holders of record and beneficial owners of shares of Common Stock must not vote or submit a proxy in favor of the Merger Proposal at the Special Meeting. A vote in favor of the Merger Proposal, in person at the Special Meeting or by proxy (whether by mail or via the internet or telephone), will constitute a waiver of appraisal rights in respect of the shares so voted and will nullify any previously filed written demands for appraisal. A stockholder exercising appraisal rights must hold of record the shares of Common Stock on the date the written demand for appraisal is made and must continue to hold the shares of record through the Effective Time. A beneficial owner exercising appraisal rights must own the shares of Common Stock on the date the written demand for appraisal is made and must continue to own such shares through the Effective Time. Accordingly, a stockholder or beneficial owner who transfers their shares prior to the Effective Time will lose any right to appraisal in respect of such shares.

Neither voting against the Merger Proposal nor abstaining from voting or failing to vote on the Merger Proposal will, in and of itself, constitute a written demand for appraisal satisfying the requirements of Section 262 of the DGCL. The written demand for appraisal must be in addition to and separate from any proxy or vote against the Merger Proposal. A stockholder’s or beneficial owner’s failure to make the written demand prior to the taking of the vote on the Merger Proposal at the Special Meeting will constitute a waiver of appraisal rights.

All written demands for appraisal of shares of Common Stock pursuant to Section 262 of the DGCL must be mailed or delivered to:

If shares of Common Stock are owned of record in a fiduciary capacity, such as by a trustee, guardian or custodian, execution of a demand for appraisal should be made by the fiduciary in that capacity. If the shares of Common Stock are owned of record by more than one person, as in a joint tenancy or tenancy in common, the demand should be executed by or for all joint owners. An authorized agent, including an authorized agent for two or more joint owners, may execute the demand for appraisal for a holder of record; however, the agent must identify the record owner or owners and expressly disclose the fact that, in executing the demand, he or she is acting as agent for the record owner.

If the Merger is completed, within 10 days after the Effective Time, the surviving corporation in the Merger will notify each record holder of shares of Common Stock who has properly and validly made a written demand for appraisal pursuant to Section 262 of the DGCL and who has not voted in favor of the Merger Proposal, and any beneficial owner who has demanded appraisal in accordance with Section 262 of the DGCL, that the Merger has become effective and the effective date thereof.

At any time within 60 days after the Effective Time, any person entitled to appraisal rights who has not commenced an appraisal proceeding or joined that proceeding as a named party, may withdraw such person’s demand for appraisal and accept the Merger Consideration by delivering to the surviving corporation in the Merger a written withdrawal of the demand for appraisal. Any attempt to withdraw such demand made more than 60 days after the Effective Time will require written approval of the surviving corporation in the Merger. No appraisal proceeding in the Delaware Court of Chancery will be dismissed as to any person without the approval of the Delaware Court of Chancery, and such approval may be conditioned upon such terms as the Delaware Court of Chancery deems just, including without limitation, a reservation of jurisdiction for any application to the Delaware Court of Chancery made under subsection (j) of Section 262 of the DGCL, provided, however, that this will not affect the right of any such person who has not commenced an appraisal proceeding or joined that proceeding as a named party to withdraw such person’s demand for appraisal and to accept the Merger Consideration within 60 days after the Effective Time. If the surviving corporation in the Merger does not approve a request to withdraw a demand for appraisal when that approval is required, or, except with respect to any person who withdraws such person’s right to appraisal in accordance with the proviso in the immediately preceding sentence, if the Delaware Court of

Chancery does not approve the dismissal of an appraisal proceeding with respect to a person, the person will be entitled to receive only the appraised value of such person’s shares of Common Stock as determined in any such appraisal proceeding, which value could be less than, equal to or more than the Merger Consideration.

Within 120 days after the Effective Time, but not thereafter, either the surviving corporation in the Merger or any person who has complied with the requirements of Section 262 of the DGCL and is entitled to appraisal rights under Section 262 of the DGCL may commence an appraisal proceeding by filing a petition in the Delaware Court of Chancery demanding a determination of the “fair value” of the shares of Common Stock held by all stockholders and beneficial owners entitled to appraisal. Upon the filing of the petition by a person other than the surviving corporation in the Merger, service of a copy of such petition will be made upon the surviving corporation in the Merger. The surviving corporation in the Merger has no obligation to file such a petition and has no present intention to file a petition, and stockholders and beneficial owners of Common Stock should not assume that the surviving corporation in the Merger will file a petition.

Accordingly, any persons who desire to have their shares appraised should initiate all necessary action to exercise and perfect their appraisal rights in respect of shares of Common Stock within the time and manner prescribed in Section 262 of the DGCL, and the failure of a person to file such a petition within the period specified in Section 262 of the DGCL could result in a loss of such person’s appraisal rights. Within 120 days after the Effective Time, any person who has properly complied with the requirements of Section 262 of the DGCL will be entitled to receive from the surviving corporation in the Merger, upon written request, a statement setting forth the aggregate number of shares of Common Stock not voted in favor of the Merger Proposal and with respect to which demands for appraisal have been received and the aggregate number of stockholders or beneficial owners holding or owning such shares. The statement must be given within 10 days after such written request has been received by the surviving corporation in the Merger or within 10 days after the expiration of the period for delivery of demands for appraisal, whichever is later. If a petition for appraisal is not filed within the time provided in accordance with Section 262 of the DGCL, then the right to appraisal with respect to the shares of Common Stock will cease.

If a petition for appraisal is duly filed by a person and a copy of the petition is served upon the surviving corporation in the Merger, then the surviving corporation in the Merger will be obligated, within 20 days after such service is made, to file with the office of the Delaware Register in Chancery in which the petition was filed a duly verified list (referred to in this summary as the “verified list”) containing the names and addresses of all persons who have demanded appraisal for their shares of Common Stock and with whom agreements as to the value of their shares of Common Stock have not been reached by the surviving corporation in the Merger. The Delaware Register in Chancery, if so ordered by the Delaware Court of Chancery, will give notice of the time and place fixed for the hearing of such petition by certified or registered mail to the surviving corporation in the Merger and to the persons shown on such list at the addresses stated therein. The forms of the notices by mail and by publication will be approved by the Delaware Court of Chancery and the costs of any such notice will be borne by the surviving corporation in the Merger.

At the hearing of such petition, the Delaware Court of Chancery will determine those persons who have complied with Section 262 of the DGCL and who have become entitled to the appraisal rights provided by Section 262 of the DGCL. Upon application by the surviving corporation in the Merger or by any person entitled to participate in the appraisal proceeding, the Delaware Court of Chancery may, in its discretion, proceed to trial upon the appraisal prior to the final determination of the persons entitled to an appraisal. Because Common Stock will be listed on the NYSE immediately prior to the Effective Time, the Delaware Court of Chancery is required under Section 262 of the DGCL to dismiss the proceedings as to all holders of such shares who are otherwise entitled to appraisal rights, unless (1) the total number of shares entitled to appraisal exceeds 1% of the outstanding shares of Common Stock or (2) the value of the consideration provided in the Merger for such total number of shares of Common Stock exceeds $1 million.

After determination of the persons entitled to appraisal of their shares of Common Stock, the Delaware Court of Chancery will conduct an appraisal proceeding in accordance with the rules of the Delaware Court of Chancery, including any rules specifically governing appraisal proceedings. Through such proceeding, the Delaware Court of Chancery will determine the “fair value” of the shares of Common Stock exclusive of any element of value arising from the accomplishment or expectation of the Merger, together with interest, if any, to be paid upon the amount determined to be the “fair value.” When the fair value is determined, the Delaware Court of Chancery will direct the payment of such value, with interest thereon, if any, to the persons entitled thereto. Such payment shall be so made to each such person upon such terms and conditions as the Delaware Court of Chancery may order. Unless the

Delaware Court of Chancery, in its discretion, determines otherwise for good cause shown, interest from the Effective Time through the date of payment of the judgment will be compounded quarterly and will accrue at 5% over the Federal Reserve discount rate (including any surcharge) as established from time to time during the period between the Effective Time and the date of payment of the judgment. At any time before the entry of judgment in the proceedings, the surviving corporation in the Merger may pay to each person entitled to appraisal an amount in cash, in which case interest shall accrue thereafter only upon the sum of (1) the difference, if any, between the amount so paid and the “fair value” of the shares as determined by the Delaware Court of Chancery, and (2) interest theretofore accrued, unless paid at that time.

You should be aware that an investment banking opinion as to the fairness, from a financial point of view, of the consideration to be received in a sale transaction, such as the Merger, is not an opinion as to “fair value” under Section 262 of the DGCL. Although we believe that the Merger Consideration is fair, no representation is made as to the outcome of the appraisal of “fair value” as determined by the Delaware Court of Chancery, and stockholders and beneficial owners should recognize that such an appraisal could result in a determination of a value higher or lower than, or the same as, the Merger Consideration. Moreover, we do not anticipate offering more than the Merger Consideration to any stockholder or beneficial owner exercising appraisal rights and reserve the right to assert in any appraisal proceeding that, for purposes of Section 262 of the DGCL, the “fair value” of a share of Common Stock is less than the Merger Consideration. In determining “fair value,” the Delaware Court of Chancery is required to take into account all relevant factors. In Weinberger v. UOP, Inc., the Delaware Supreme Court discussed the factors that could be considered in determining “fair value” in an appraisal proceeding, stating that “proof of value by any techniques or methods which are generally considered acceptable in the financial community and otherwise admissible in court” should be considered and that “[f]air price obviously requires consideration of all relevant factors involving the value of a company.” The Delaware Supreme Court has stated that in making this determination of “fair value,” the Delaware Court of Chancery must consider market value, asset value, dividends, earnings prospects, the nature of the enterprise and any other facts that were known or that could be ascertained as of the date of the merger that throw any light on future prospects of the merged corporation. Section 262 of the DGCL provides that “fair value” is to be “exclusive of any element of value arising from the accomplishment or expectation of the merger.” In Cede & Co. v. Technicolor, Inc., the Delaware Supreme Court stated that such exclusion is a “narrow exclusion [that] does not encompass known elements of value,” but that rather applies only to the speculative elements of value arising from such accomplishment or expectation. In Weinberger, the Delaware Supreme Court also construed Section 262 of the DGCL to mean that “elements of future value, including the nature of the enterprise, which are known or susceptible of proof as of the date of the merger and not the product of speculation, may be considered.”

Costs of the appraisal proceeding (which do not include attorneys’ fees or the fees and expenses of experts) may be determined by the Delaware Court of Chancery and taxed upon the parties by the Delaware Court of Chancery, as it deems equitable in the circumstances. Each person seeking appraisal is responsible for their attorneys’ and expert witness expenses; although, upon the application of a person whose name appears on the verified list who participated in the proceeding and incurred expenses in connection therewith, the Delaware Court of Chancery may order all or a portion of such expenses, including, without limitation, reasonable attorneys’ fees and the fees and expenses of experts used in the appraisal proceeding, to be charged pro rata against the value of all shares of Common Stock entitled to appraisal not dismissed pursuant to subsection (k) of Section 262 of the DGCL or subject to such an award pursuant to a reservation of jurisdiction.

From and after the Effective Time, no person who has demanded appraisal rights with respect to some or all of such person’s shares of Common Stock in compliance with Section 262 of the DGCL will be entitled to vote shares of Common Stock for any purpose or to receive payments of dividends or any other distribution with respect to those shares of Common Stock (except dividends or other distributions payable to stockholders of record at a date which is prior to the Effective Time).

If no petition for appraisal is filed within 120 days after the Effective Time, then the right of all persons to appraisal will cease and such persons’ shares of Common Stock will be deemed to have been converted at the Effective Time into the right to receive the Merger Consideration, without interest and less any applicable withholding taxes. A person will fail to perfect, or effectively lose, the right to appraisal if no petition for appraisal is filed within 120 days after the Effective Time. In addition, as described above, a person may withdraw his, her or its demand for appraisal in accordance with Section 262 of the DGCL at any time within 60 days after the Effective Time (or thereafter with the written approval of Atkore) and accept the Merger Consideration, without interest and

less any applicable withholding taxes. Once a petition for appraisal has been filed with the Delaware Court of Chancery, however, the appraisal proceeding may not be dismissed as to any person without the approval of the Delaware Court of Chancery, and such approval may be conditioned upon such terms as the Delaware Court of Chancery deems just, including without limitation, a reservation of jurisdiction for any application to the Court made under Section 262(j) of the DGCL. However, that restriction will not affect the right of any person who has not commenced an appraisal proceeding or has not joined the appraisal proceeding as a named party to withdraw such person’s demand for appraisal and to accept the Merger Consideration, without interest and less any applicable withholding taxes, within 60 days after the Effective Time. Failure to comply strictly with all of the procedures set forth in Section 262 of the DGCL will result in a loss of statutory appraisal rights. Because of the complexity of Section 262 of the DGCL, holders of record and beneficial owners of shares of Common Stock who may wish to pursue appraisal rights should consult their legal and financial advisors.

To the extent there are any inconsistencies between the foregoing summary of procedures under Section 262 of the DGCL and Section 262 of the DGCL, Section 262 of the DGCL will govern.

Shares of Common Stock are listed for trading on the NYSE under the symbol “ATKR.” On July 31, 2026, the last trading day prior to the public announcement of the Merger, the closing price for the shares of Common Stock on the NYSE was $72.96 per share. On    , 2026, the most recent practicable date before the date of this proxy statement, the closing price for the shares of Common Stock on the NYSE was $    per share. For current price information, you are urged to consult publicly available sources.

Atkore paid a total of $1.30 in cash dividends per share of Common Stock during the 12 months ended September 30, 2025. On November 18, 2025, the Board declared a quarterly cash dividend of $0.33 per share of Common Stock, payable on December 17, 2025, to stockholders of record as of December 5, 2025. On January 28, 2026, the Board declared a quarterly cash dividend of $0.33 per share of Common Stock, payable on February 27, 2026, to stockholders of record as of February 17, 2026. On April 30, 2026, the Board declared a quarterly cash dividend of $0.33 per share of Common Stock, payable on May 29, 2026, to stockholders of record as of May 19, 2026. On July 30, 2026, the Board declared a quarterly cash dividend of $0.33 per share of Common Stock, payable on August 28, 2026, to stockholders of record as of August 18, 2026.

Pursuant to the Merger Agreement, Atkore may not, without Prysmian’s prior written consent, declare, set aside, authorize or pay any dividend or distribution on the Common Stock during the period from the date of the Merger Agreement through the Effective Time, other than regular quarterly dividends in an amount no greater than $0.33 per share per quarter, paid at such times and in a manner consistent with Atkore’s historical quarterly dividend practice.

As a result of the Merger, following the Effective Time, the Common Stock will no longer be publicly traded, will be delisted from the NYSE and will be deregistered under the Exchange Act.

As of    , 2026, there were     outstanding shares of Common Stock, and there were     record holders of shares of Common Stock.

The information provided below sets forth certain information as of August 21, 2026, regarding (i) the ownership of voting securities of Atkore by each person who is known to the management of Atkore to have been the beneficial owner of more than 5% of the outstanding Common Stock, (ii) the ownership interest of each director of Atkore, (iii) the ownership interest of each named executive officer of Atkore and (iv) the ownership interest of executive officers and directors of Atkore as a group. Insofar as is known to Atkore, each such person, entity or group has sole voting and dispositive power with respect to all such shares of Common Stock, except as otherwise noted.

For purposes of the tables below, the amounts and percentages of Common Stock beneficially owned are reported on the basis of regulations of the SEC governing the determination of beneficial ownership of securities. Under the rules of the SEC, a person is deemed to be a “beneficial owner” of a security if that person has or shares “voting power,” which includes the power to vote or to direct the voting of such security, or “dispositive power,” which includes the power to dispose of or to direct the disposition of such security. A person is also deemed to be a beneficial owner of any securities of which that person has a right to acquire beneficial ownership within 60 days, including through the exercise of options or warrants. Beneficial ownership also includes securities that are the subject of a voting trust, proxy, power of attorney or other similar agreement. Under these rules, more than one person may be deemed a beneficial owner of the same securities and a person may be deemed a beneficial owner of securities as to which they have no economic interest.

Percentage computations are based on 33,772,550 shares of Common Stock outstanding as of August 21, 2026.

Except as otherwise indicated in these footnotes, each of the beneficial owners listed has, to Atkore’s knowledge, sole voting and investment power with respect to the indicated shares of Common Stock. Unless otherwise set forth in the footnotes to the table, the address for each listed stockholder is c/o Atkore Inc., 16100 South Lathrop Avenue, Harvey, IL 60426.