2a spring/detent kit builder series ar15 black! FEATURES:-Includes: Buffer Retainer, Buffer Retainer Spring, Bolt Catch Plunger, Bolt Catch Spring, SelectorDetent Pin, Selector Detent Spring, Detent Pivot Pin X2, Detent Pivot Spring X2 Other Features: Spare detents and springs for ar15/ar10, buffer retainer and spring, bolt catch plunger and spring, selector detent pin and spring detent pivot pin x2, detent pivot pin spring x2