Bolt carrier group (auto version) f your AR15, M16, or M4. Parkerized exterior and chrome lined inside carrier. Machined to USGI specifications. This M16/M4 carrier includes the proper Mil-Spec gas key. Gas key is chrome lined and heat treated per GI specifications. Gas key is secured to 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.The bolt assembly is shot peened for increased strength, includes tool steel machined extractor, BCM Extractor Spring, and is MPI (Magnetic Partical Inspected).SPECS:MPI Bolt (Magnetic Particle Inspected) Shot Peened Bolt Chrome Lined Carrier (AUTO)Chrome Lined Gas KeyGas Key Hardened to USGI SpecificationsGrade 8 Hardened FastenersKey Staked Per Mil-SpecBCM Extractor SpringBlack Extractor Insert