SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

Atkore International Group Inc.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

047649 10 8

(CUSIP Number)

December 31, 2017

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

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CUSIP No. 047649 10 8

Atkore International Group Inc. (the “Issuer”)

16100 South Lathrop Avenue

Harvey, Illinois 60426

(708) 339-1610

CD&R Allied Holdings, L.P.

CD&R Associates VIII, Ltd.

CD&R Associates VIII, L.P.

CD&R Investment Associates VIII, Ltd.

CD&R Allied Holdings, L.P., CD&R Associates VIII, Ltd., CD&R Associates VIII, L.P. and CD&R Investment Associates VIII, Ltd., have entered into a Joint Filing Agreement, dated February 9, 2018, a copy of which is filed with this Schedule 13G as Exhibit 99.1, pursuant to which such reporting persons have agreed to file this statement jointly in accordance with the provisions of 13d-1(k)(1) under the Securities Exchange Act of 1934.

CD&R Allied Holdings, L.P.

P.O. Box 309, Ugland House, South Church Street,

George Town, Grand Cayman, KY1-1104

Citizenship: Cayman Islands

CD&R Associates VIII, Ltd.

P.O. Box 309, Ugland House, South Church Street,

George Town, Grand Cayman, KY1-1104

Citizenship: Cayman Islands

CD&R Associates VIII, L.P.

P.O. Box 309, Ugland House, South Church Street,

George Town, Grand Cayman, KY1-1104

Citizenship: Cayman Islands

CD&R Investment Associates VIII, Ltd.

P.O. Box 309, Ugland House, South Church Street,

George Town, Grand Cayman, KY1-1104

Citizenship: Cayman Islands

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See Item 2(b) above.

Common Stock, par value $0.01 per share

047649 10 8

(a) [ ] Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);

(b) [ ] Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);

(c) [ ] Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);

(d) [ ] Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8);

(e) [ ] An investment adviser in accordance with §240.13d-1(b) (1)(ii)(E);

(f) [ ] An employee benefit plan or endowment fund in accordance with §240.13d-1(b) (1)(ii)(F);

(g) [ ] A parent holding company or control person in accordance with §240.13d-1(b) (1)(ii)(G);

(h) [ ] A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i) [ ] A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j) [ ] A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J);

(k) [ ] Group, in accordance with § 240.13d-1(b)(1)(ii)(K).

Not Applicable.

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

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As of the dates listed in the table below, each of the Reporting Persons beneficially owned the number and percentage of issued and outstanding shares of common stock of Atkore International Group Inc. listed opposite its name:

Investment and voting decisions with respect to shares held by CD&R Allied Holdings, L.P. are made by an investment committee of limited partners of CD&R Associates VIII, L.P. (the “Investment Committee”). The CD&R investment professionals who have effective voting control of the Investment Committee are Michael G. Babiarz, Vindi Banga, James G. Berges, John C. Compton, Kevin J. Conway, Russell P. Fradin, Thomas C. Franco, Kenneth A. Giuriceo, Donald J. Gogel, Jillian Griffiths, Marco Herbst, Sarah Kim, John Krenicki, Jr., David A. Novak, Paul S. Pressler, Roberto Quarta, Christian Rochat, Eric Rouzier, Ravi Sachdev, Steven W. Shapiro, Richard J. Schnall, Nathan K. Sleeper, Derek Strum, David H. Wasserman and J.L. Zrebiec. All members of the Investment Committee disclaim beneficial ownership of the shares shown as beneficially owned by the funds associated with Clayton, Dubilier & Rice, LLC.

28.5%^*

(i) Sole power to vote or to direct the vote:

0

(ii) Shared power to vote or to direct the vote:

The Filers may be deemed to have shared power to vote or direct the vote of 13,234,838 shares of common stock. Each of the Filers disclaim such beneficial ownership of such shares.

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(iii) Sole power to dispose or to direct the disposition:

0

(iv) Shared power to dispose or to direct the disposition:

The Filers may be deemed to have shared power to dispose or direct the disposition of 13,234,838 shares of common stock. Each of the Filers disclaim such beneficial ownership of such shares.

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [    ]:

Not Applicable.

Not Applicable.

Not Applicable.

Not Applicable.

Not applicable.

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Signatures

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: February 9, 2018

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Exhibit 99.1

AGREEMENT REGARDING THE JOINT FILING OF SCHEDULE 13G

The undersigned hereby agree as follows:

Date: February 9, 2018