BCM bolt carrier group auto version for your AR15, M16, or M4. Parkerized exterior and chrome lined inside the carrier. Machined to USGI specifications. This M16/M4 carrier includes the proper Mil-Spec gas key. The gas key is chrome lined and heat treated per GI specifications. The gas key is secured to the carrier via USGI domestic mfg Grade 8 fasteners and properly staked per Mil-Specs. These properly hardened parts insure a strong staking and proper gas system functioning.