The S&W M&P Essentials Parts Kit contains all those tiny pieces that are often broken or lost. Kit includes Bolt Catcher Plunger, Bolt Catch Spring, Bolt Catch Roll Pin, Buffer Retainer, Buffer Retainer Spring, Disconnector Spring, Hammer Spring, Trigger Spring, Hammer Pin, Trigger Pin, Pivot Pin Detent, Pivot Pin Detent Spring, Takedown Pin Detent, Takedown Pin Detent Spring, Selector Detent, Selector Detent Spring, Trigger Guard Roll Pin and Magazine Catch Spring.