Customization is endless with the AR15 platform which is why the CMMG ZEROED Mk4/AR15 Gunbuilder's Kit includes all of the essential parts except the most commonly upgraded ones: Trigger Guard Fire Control Group and Pistol Grip. Check out our interactive install walkthrough video below or read the CMMG Resources LPK Install article for an in-depth breakdown. All parts meet or exceed mil-spec. All installation hardware included.Kit Includes: Bolt Catch Plunger Spring & Roll Pin Trigger/Hammer Retaining Pins ZEROED 60Adeg/90Adeg Adjustable Ambi Safety Detent & Spring ZEROED Ambi Magazine Catch & Spring ZEROED Magazine Release Button HD Pivot/Takedown Pins Detents & Springs Buffer Retainer & Spring