Bolt carrier, Machined from S7 Tool Steel, Lithium Isonite Coating, 4 Setting Adjustable Vent System relieves excess gas pressure created from suppressor use creating longer dwell time and less blowback to the shooter. Gas Adjustment can be turned while installed in the rifle, Staked MIL-SPEC Gas Key, Adjustment Pin is easily removed for cleaning. This carrier does not come complete. This follows the DPMS Gen 1 Pattern for the AR-10 design. The AR-10 does not have MIL-SPEC sizing