TRYBE Defense AR-15 Mil-Spec Bolt Assembly Completion Group is a nickel boron coated bolt assembly kit for AR-15 Mil-Spec builds. This kit includes a bolt assembly, firing pin, cam pin, and firing pin retaining pin. Bolt components are manufactured to Mil-Spec tolerances; extractor is nickel boron coated. Caliber: 5.56x45mm NATO. Color: Nickel Boron. Made in the USA. Includes: Bolt Assembly Completion Group, Firing Pin, Cam Pin, Firing Pin Retaining Pin.