SUBSEQUENT EVENTS	9 Months Ended
Jun. 26, 2026
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	19. SUBSEQUENT EVENTS On July 6, 2026, the Company paid Infra Pipes $13,000 to settle the outstanding portion of its cash funding commitments related to the HDPE divestiture. See Note 3, “Divestitures” and Note 16, “Commitments and Contingencies” for details. On July 30, 2026, Atkore’s Board of Directors approved a quarterly dividend payment of $0.33 per share of common stock payable on August 28, 2026 to stockholders of record on August 16, 2026. On August 2, 2026, Atkore entered into an Agreement and Plan of Merger (the “Merger Agreement”) with 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 (the “Guarantor”), pursuant to which, at the closing of the transactions contemplated by the Merger Agreement, Merger Sub will merge with and into Atkore, with Atkore surviving as a wholly owned subsidiary of Prysmian (the “Merger”). Pursuant to the Merger Agreement, at the effective time of the Merger (the “Effective Time”), each share of Atkore’s common stock issued and outstanding immediately prior to the Effective Time (subject to certain customary exceptions specified in the Merger Agreement) will be converted into the right to receive $95.00 per share in cash, without interest. The consummation of the Merger is subject to the satisfaction or waiver of customary closing conditions, including, among others, the adoption of the Merger Agreement by the affirmative vote of the holders of a majority of the outstanding shares of Atkore’s common stock entitled to vote thereon at a meeting of Atkore’s stockholders duly called and held for such purposes, the expiration or termination of applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 and the receipt of certain regulatory approvals. Prysmian’s obligations are also conditioned upon the absence of any material adverse effect since the Merger Agreement. The Merger Agreement also contains customary representations, warranties and covenants by each of Prysmian, Merger Sub and Atkore and certain representations, warranties and covenants by the Guarantor, including, among others, covenants by Atkore to use commercially reasonable efforts to conduct its business in all material respects in the ordinary course and, to the extent consistent therewith, to preserve in all material respects its business organization, material assets and properties and maintain its existing material relationships and goodwill, and to refrain from taking certain specified actions without the consent of Prysmian.

On August 2, 2026, Atkore entered into an Agreement and Plan of Merger (the “Merger Agreement”) with 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 (the “Guarantor”), pursuant to which, at the closing of the transactions contemplated by the Merger Agreement, Merger Sub will merge with and into Atkore, with Atkore surviving as a wholly owned subsidiary of Prysmian (the “Merger”). Pursuant to the Merger Agreement, at the effective time of the Merger (the “Effective Time”), each share of Atkore’s common stock issued and outstanding immediately prior to the Effective Time (subject to certain customary exceptions specified in the Merger Agreement) will be converted into the right to receive $95.00 per share in cash, without interest.

The consummation of the Merger is subject to the satisfaction or waiver of customary closing conditions, including, among others, the adoption of the Merger Agreement by the affirmative vote of the holders of a majority of the outstanding shares of Atkore’s common stock entitled to vote thereon at a meeting of Atkore’s stockholders duly called and held for such purposes, the expiration or termination of applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 and the receipt of certain regulatory approvals. Prysmian’s obligations are also conditioned upon the absence of any material adverse effect since the Merger Agreement. The Merger Agreement also contains customary representations, warranties and covenants by each of Prysmian, Merger Sub and Atkore and certain representations, warranties and covenants by the Guarantor, including, among others, covenants by Atkore to use commercially reasonable efforts to conduct its business in all material respects in the ordinary course and, to the extent consistent therewith, to preserve in all material respects its business organization, material assets and properties and maintain its existing material relationships and goodwill, and to refrain from taking certain specified actions without the consent of Prysmian.