The FailZero AR-15 Bolt Carrier Group comes fully assembled and ready to drop into most properly chambered Mil-Spec upper receivers. All critical parts are coated with EXO Nickel Boron technology that provides permanent dry lubricity, extreme durability and increases both wear and corrosion resistance. EXO Nickel Boron makes for easy cleanup and will improve the performance of your rifle. The extractor hardware includes a heavy spring, silicone insert, and o-ring to give better extraction tension. Nickel Boron treated parts include:Bolt & ExtractorM16 Cut Bolt CarrierCam PinCarrier KeyFiring Pin