Lantac M-SPEC Upper Parts Kit (UPK) for AR15 style rifles. Manufactured to the highest quality standards using correct materials, heat treatments and finishes to comply with up to date military specifications. Kit includes the following: Bolt Catch Plunger Bolt Catch Plunger Spring Bolt Catch Roll Pin Bolt Catch Set Screw (6-32, compatible with Lantac , Aero and other lowers). 1/16th Allen Key Head Buffer Retainer x2 Buffer Retainer Spring x2 Takedown Pin Detent x2 Takedown Detent Spring x2 Pivot Pin Detent x2 Pivot Pin Detent Spring x2 Trigger Pin x2 Safety Selector Detent x2 Safety Selector Detent Spring x2