Yes, that's one half of a half-cheek, jointed snaffle bit. Almost certainly used on a harness horse, where a half-cheek is most common. A riding horse may also go in a snaffle, but it would be a ring (more common) or full-cheek style. Quite a fancy cheekpiece- that wasn't a regular workaday field harness. Though I can't tell the side for sure, I'm guessing it's a 4-5" bit (which are measured from inside of the cheekpiece to the opposite cheekpiece. Which would mean it was used on a light carriage horse, not a draft farm horse (whose bit would be much larger, 6-7")