Last one needing help to identify:

this gas cap is vented in the center domed with a light knurled edge. Appears to be a heavy skin over a steel base. Could be chrome or nickel plated. This one is approx 3/4" high and 3-3/4" dia. with a bayonnet for holding to a tank ao approx 1-1/2" dia.

Thanks for all your help with these four items.