CMMG Gun builders kit includes most of the necessary parts to build up your lower group except the commonly upgraded parts. Does not include Trigger Guard, Fire Control Group, and pistol grip. All parts meet or excede mil-spec.Specifications and Features: Bolt Catch Bolt Catch Plunger Bolt Catch Roll Pin Bolt Catch Spring Buffer Retainer Buffer Retainer Spring Hammer Pin Magazine Catch Magazine Catch Button Magazine Catch Spring Pivot Pin Pivot Pin Detent Pivot Pin Detent Spring Selector Selector Detent Selector Detent Spring Takedown Pin Takedown Pin Detent Takedown Pin Detent Spring Trigger Pin