California Code, Health and Safety Code - HSC § 13025

(a) All equipment for fire protection purposes having couplings or fittings with an inside diameter of three inches or less, purchased by any authorities having charge of public property, shall be equipped with standard threads for fire hose couplings and hydrant fittings designated as the national standard as adopted by the National Board of Fire Underwriters, which standard is designated as the standard for such equipment in this state. The State Fire Marshal shall adopt and submit building standards for approval pursuant to Chapter 4 (commencing with Section 18935) of Part 2.5 of Division 13 of this code in order to conform such building standards to the provisions of this subdivision and subdivision (b).

(b) All equipment for fire protection purposes having couplings or fittings with an inside diameter greater than three inches, if equipped with threads, shall be equippped  1 with the standard threads prescribed in subdivision (a).

(c) All equipment for fire protection purposes having couplings or fittings with an inside diameter greater than three inches not equipped with threaded fittings or couplings shall be approved by the State Fire Marshal, with advice from the State Board of Fire Services. The proposed system of use of such nonthreaded couplings or fittings shall be submitted in detail to the State Fire Marshal who shall, with advice from the State Board of Fire Services, approve its use if mutual aid capability is assured.

(d) The State Fire Marshal shall adopt and submit building standards for approval pursuant to the provisions of Chapter 4 (commencing with Section 18935) of Part 2.5 of Division 13 of this code for any fire hydrants, including dry standpipe connections, in or on any improvement to land, which building standards define the requirements for standard threads for fire hose couplings and hydrant fittings as provided in subdivision (a) or (b).