Original Style flip top LeMans Roller Latch Polished Gas cap is a 2 piece universal fit and is very popular on 1965-1968 Mustang, designed with a roller quick release latch and threaded flange that is not drilled for easy mounting to desired location..
Also used on AC Cobras, GT500 E/ Shelby and other Muscle cars.
For filler neck see part # EXT-000-577
(Threaded 5" O.D flange base that requires drilling mounting holes with 3-1/4" I.D. The top measures 4-3/4" round, overall is approximately 6-3/8" and 2-1/2" tall.)