The M&P Customizable lower parts kit is the ideal choice if you want to build a custom AR-15. This kit provides all the minor parts generally used in an AR-15 build, but allows the flexibility to add popular common aftermarket upgrades. The kit includes a bolt catch, plunger, roll pin and spring; buffer retainer and spring; hammer pin; magazine catch, button, and spring; pivot pin, pin detent, and pin detent spring; selector detent and spring; takedown pin, pin detent, and pin detent spring; and trigger pin.