-Fits AR-15/M4 compatible style rifles-Mil-spec dimensions-Bolt Carrier Group Material: Case hardened 8620-Steel Finish: Black nitride-Gas Key: 4130 steel attached with Grade 8 hardware & properly staked into a milled "valley" to ensure proper positioning-Cam Pin: Hardened 4340 cam pin-Firing Pin: Mil-Spec firing pin made of 8740 steel, center-less ground & hard chrome coated-Bolt Assembly: The bolt is "true" Mil-Spec dimension & external surfaces are CNC ground-Bolt Material: Case hardened 9310 steel-Finish: All bolt components black nitride-Extractor: 4340 steel Mil-Spec-Extractor spring &O-ring combination-Magnetic Particle Inspected-High Pressure Test-Made in USA