It's 3-1/8" wide. The ends are fastened on; they don't screw off. Sweater button-hole-closer thingy? I'm thinking not a collar stay given the width and the fact that the end doesn't come off, but WDIK.
It looks like a jabot pin, but the ends stay on? It might be the ladies equivalent of one of those guys tie bars - the ones that go up at the neck to make sure things lay right. The ends look like rhinestone-embedded bakelite.
I stand corrected. I had tried to pull the ends off previously to see if it was a pin; I didn't even try unscrewing them. One side does unscrew and has a pinpoint end, so I think jabot is right on target! Thanks evelyb!
Welcome. These turn up on a regular basis if you "do" old jewelry. A lot of them are celluloid or bakelite, but I had one here that looked like a darning egg. I had to ask the first time too.
