Metal Cap for Rad? Gas? Steering Wheel?

This cap looks familiar, but can't quite place it.

About the size of a gas tank or radiator cap, but the threaded mount seems odd unless early 30's or older. May be a steering wheel center cap or some other application.

The cap is made of heavy stamped metal with nice chrome plating. Around 1 inch high with a shallow domed top. Overall diameter is about 3 1/2 inches and there are 5 styling bumps equally spaced around the rim. It mounts by an insert about 2 1/4 inch diameter with external threads.

I have about 20 of these from a lot of old parts from 1930's - 1960's, so would really like to identify.

Hope someone recognizes!