It is definitely part of a horse bridle bit, known as a "snaffle bit" if I recall correctly. They've been in use for so many centuries that there's no way to date them with much accuracy -- nor to know if one is military-used or civilian unless it has a Military marking. See an intact one in the photo below.
Edit: Creskol and I were typing at the same time. Took me a bit longer, to find and add the photo.
Ha yep and stop that baby. It causes their head to come up hopefully making them stop lol. A horse I worked with once would turn his head and up and go the opposite direction and hated that damn thing he was great with a hackamore of course lol
There are copper tasters also. The old Spanish spade bits had copper in the mouth, and a lot of modern bits do also. Supposed to be a taste thing and it also is supposed to keep the horses mouth moist.