San Tan Tactical 17-part lower parts kit is a MIL-SPEC LPK for building your AR-15 lower receiver. This 17-piece kit includes the following: bolt catch, bolt catch plunge, bolt catch spring, bolt catch roll pin, mag release, mag release button, mag release spring, buffer retainer spring, safety, buffer retainer, buffer detent spring, safety detent, trigger guard, trigger guard roll pin, takedown detent springs, takedown detents, takedown pins.