Results of Operations

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549   FORM 8-K CURRENT REPORT   Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of Report (Date of earliest event reported): April 21, 2020 MUELLER INDUSTRIES INC . (Exact name of registrant as specified in its charter)   Delaware 1-6770 25-0790410 (State or other jurisdiction (Commission File (IRS Employer of incorporation) Number) Identification No.)    150 Schilling Boulevard Suite 100 Collierville Tennessee 38017 (Address of principal executive offices) (Zip Code) Registrant’s telephone number, including area code: (901) 753-3200 Registrant’s Former Name or Address, if changed since last report: N/A   Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below): ☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)  ☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)  ☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))  ☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))  Securities registered pursuant to Section 12(b) of the Act: Title of each class Trading Symbol Name of exchange on which registered Common Stock MLI NYSE    Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new of revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐   Item 2.02. Results of Operations and Financial Condition. On  April 21, 2020 , the Registrant issued a press release announcing earnings for the quarter ended  March 28, 2020 . A copy of the press release announcing the  first quarter  2020 earnings is attached as Exhibit 99.1. Item 9.01. Financial Statements and Exhibits.   (d) Exhibits     99.1 Press release, dated April 21, 2020 reporting first quarter 2020 earnings.                                   2   SIGNATURES   Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this Report to be signed on its behalf by the undersigned hereunto duly authorized.     MUELLER INDUSTRIES, INC.       By: / s/   JEFFREY A. MARTIN     Name: Jeffrey A. Martin   Title: Chief Financial Officer and Treasurer       April 21, 2020         3 Exhibit Index   Exhibit No. Description      99.1 Press release, dated April 21, 2020.                                     4