Manufactured by our finest domestic, Mil-Spec contractors these are among the best AR rifle bolts on the market and the same bolt carrier groups we use as the basis of our renowned custom rifles!The bolt is precision machined from aerospace grade 9310 tool steel, shot peened for increased strength and includes a tool steel extractor and ejector, appropriate extractor spring, and is MPI (Magnetic Particle Inspected) and randomly batch HPT (High Pressure Tested).The extractor is 4140 gun quality, annealed, cold drawn steel per the Mil-Spec.With a complete phosphate finish, the 8620 steel carrier includes a proper machined Mil-Spec gas key secured to the carrier via Grade 8 fasteners and properly staked in our shop during final inspection.These precisely machined, finished and hardened parts will ensure long term proper gas system functioning and reliability.All experienced AR shooters know that the best spare parts kit for an AR-15 rifle is a spare complete bolt carrier assembly!NOTE- The only difference between "semi-auto" and "full-auto" carriers are the carrier weight and external profile. The "full-auto" carrier is slightly heavier to provide more mass and lower cyclic rate that can benefit carbine length and shorter gas systems, short barreled/suppressed rifles and machine guns. The "semi-auto" carrier is slightly lighter to provide the least amount of recoil impulse for rifle length gas systems and it's design makes reinstalling the firing pin easier after cleaning.Both carrier types are considered completely interchangeable and there are no restrictions on the ownership of a "full auto" carrier group in a semi-automatic rifle.Features: Bolt material is aerospace grade 9310 MPI inspected Mil-Spec parts ensure a long service life Machined ejector and extractor per mil specs Full Auto carrier (see note) Drop in fit for any quality 5.56 case head based AR rifle (.223/5.56 NATO, .300 Blackout, .204 Ruger,300 HAM'R, or 7.62X40 WT)