Doublestar Corp. Bolt Carrier Group Chrome Lined Includes O Ring AR100This complete bolt-and-carrier group easily drops into a standard mil-spec AR-15 upper and it's ready to shoot. Batch magnetic particle inspected bolt gives long service life. Bolt and carrier feature a matte black phosphate finish that resists heat wear and corrosion. Carrier is chrome lined and has a staked gas key. Includes bolt assembly firing pin firing pin retaining pin cam pin and complete carrier.