Hi!
This is going to be a post civil war cavalry insignia. If the coloring is bronze and not a yellow brass it will be a 20th century piece. Civil war pieces are stamped so they are hollow on the back with soldered U shaped fasteners. Civil war are also thicker scabbards and 3 inches wide. Post war the scabbard are skinnier and the insignia smaller to fit on collars. These types show up around the turn of the century and given that this might be bronze colored it would be very similar to ww1 collar discs