These are replacement snap rivets for Crocks and similar, unforgivably ugly footwear. The thinner male one goes on the inside through the smaller hole, the female end goes through the larger hole from the outside. Just push to snap, and pull to unsnap.

I printed mine with PETG and am about to give them a walkabout to see how they wear.

These are not compatible with the factory snaps, so you can't use a male from one and a female from the other.