Here are four different button covers. They would have been made in sets of four or six originally. I think they were popular in the 1980s or thereabouts. They were made to convert a very plain button on a garment to something dressier thus altering the look of a jacket for example. The cover opens up and the back slides behind the original button and then clips shut. I have quite a few different ones but only a couple of full sets. I wonder who came up with the idea; quite ingenious.