This is an original US WW1-era 'Pederson' Belt Pouch, designed to hold five 40-round Magazines of .30 caliber pistol rounds. The Pedersen Device converted the 1903 Springfield Rifle to fire the .30 caliber rounds semi automatically. (Last photo shows amuseum example of a complete kit. This is an unissued example (with some minor storage stains) from the Rock Island Arsenal.