The twist on fuel cap you need is D1ZZ-9030-A (ID# D1ZA-AA, AB, AC) and would have Autolite on the reverse side. Since Ford was transitioning to the Motorcraft brand from late '71 into '72, some early '72 caps could have the Autolite brand but have the '72 ID number. Those caps were D2ZZ-9030-A (ID# D2ZA-AA, AB). For a short time, a D3ZZ-9030-A (D3ZA-AA) fuel cap was used for the '73 Mustangs but was reverse-replaced by the reinstated D2ZZ-A. Of course, those would have Motorcraft branding.
The flip-open fuel cap was exclusive to Mach 1. There was no stand-alone option for this type of cap on the other models. Ford was taking some heat from the Government over the cap's design. During some accidents and rollovers, the cap was not sealing as well as the twist on caps and, in some instances, was popping open and spilling fuel. Ford revised the '71 cap four times and did not resolve the leaking problem. All the revised 72 sales brochures and order guides (as of 1/72) show the twist-style cap on Mach 1. Since several new emissions and safety-related laws were going into effect on January '72, I can only assume that is when Ford changed the cap and got the Feds off their back.
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