Hello all, got to one of my permissions today for a bit of digging. This rang up 17 on my nox which is usually bottle tops and such... was pleasantly surprised with this one. The pin actually swivels nicely.
As already said, it could be from a suspender. I found something very similar, and it was a waist adjuster, so I suppose that is a possibility too. Late 1800s or early 1900s seems about right to me. Congrats!