Odin Works AR15 Black Nitride Bolt Carrier Group has Mil-Spec dimensions with a low friction coating that minimizes the need for lubricants. Features: a Gas Key: 4130 Steel attached with Grade 8 hardware and properly staked into a milled "valley" to ensure proper positioning. a Cam Pin: Hardened 4340 cam pin a Firing Pin: Mil Spec firing pin made of 8740 steel, center-less ground and Hard Chrome coated a Bolt Assembly: The Bolt is "true" Mil Spec dimension and external surfaces are CNC ground after heat treat for a precision fit. a Made in the USA