We made the embossed caps for the 1935 and 1936 Ford cars and lo' and behold it turns out they fit the 1935 and 1936 Chevy cars and a myriad of other vehicles too.

This is the conventional size and fits a variety of other vehicles that  utilize the inverted cup that rides a "formed ramp" until it strikes the downward facing tab stop.  Its commonly called a bayonet-style cap and was used with with non pressure systems. 

We have tested these and we estimate that the fiberboard seal and inverted shallow brass cup behind it create a resistance of ~3psi.  It is intended for non pressure systems