This single strap brown (maybe black) buff leather frog was made to carry a bayonet or sword with a round or oval frog stud on the throat mount. It was found on a Sharps Model 1859 US Navy Mitchell Contract Bayonet (ER# 1819) and it appears to have been together for some time.
It is a crude production from two pieces of unfinished leather with the buff side out. The base piece is simply folded over and stitched to form the belt loop. The second piece is double stitched to the base piece on both edges to form the pocket. A hole was cut to accept the frog stud. Possibly a field replacement?
It is 215 millimeters long and 88 millimeters wide.