The USM8A1 is primarily a bayonet scabbard, not a bayonet itself, made from olive drab webbing/plastic with a metal throat and M1910 wire hanger, designed to hold various US bayonets (M4, M5, M6, M7) and the M3 fighting knife. Key features include a snap-retaining strap and leather leg thong, with variations in manufacturers (PWH, TWB, BMCo, VPCo) and minor design tweaks like metal tip reinforcement and hanger changes over time, making it a common accessory for Vietnam-era and post-war rifles.