This is a knife/sword bayonet manufactured beginning 1917 and was used on several firearms to WWII. They are very similar to their predecessors: the British P1907 (muzzle-ring is closer to the blade rib and does not have U.S. markings) and the US/British Model 1913/17 (has the same dimensions, but does not have the U.S. Ordnance Bomb on the ricasso). The Model 1913/17 will interchange with the Model 1917 but not with the P1907. These were manufactured for the U.S. "Enfield" or "Eddystone" .303" caliber rifle (not to be confused with the British No.1 SMLE series which accepts the British P1907 Bayonet).