Anyone collect us em cap badges

[SADolch]

Anyone collect these badges,I have quite a few and was wondering how many different types were made and how do you know what era they are from,here are a few to start.................Dave H

[gel65]

There are some many types made from ww1 to the 1950s there are models for the ww1 period ones, the badge in the wrapping looks like 50s era, the rest are
ww2 era nice lot