Re: Odd Pin Back's, what are these?
Yes, it is one side of some type of ladies jewelry 'clip.' Depending on how it operates would depend on what type of clip it is. I'm assuming the 2 side pieces fold upward to fit inside of a sweater button hole, then spread back out to hold it in place. If this is how it operates, it's a sweater clip probably from the 1950s. If the mechanisms open outward, then it could be a hair clip. Can you post other pics and/or describe how the mechs work? Interesting find, Breezie