Fuel caps as OEM replacement

Depending on the year and model, the caps differ in diameter and thread. Up to 1936, right-hand thread 1.5”-24, from 1983 right-hand thread 1.75”-4 on all positions except the left tanks of FLH and Softail. These have the same pitch and diameter, but a left-hand thread. From 1936-1982, tanks had a bayonet lock, depending on the year of manufacture at different heights. Sometimes you can make do with different thicknesses of seals, often you can get on faster with measuring and comparing.