Standard mil-spec AR-15 lower parts kit. This kit can be used in any mil-spec AR-15 lower receiver (2.23, 5.56, 9mm, 40S&W and 45ACP caliber builds.) Please note: if you are purchasing this kit for our 0940 or 1045 receivers you will not use the supplied bolt catch spring or bolt catch roll pin. You need to use the lightened spring kit included with the receiver. Lower Parts Kit (LPK) includes: Pistol grip with grip screw Trigger Trigger Spring Trigger/Hammer Pin (2) Hammer Hammer Spring Disconnector Disconnector Spring Selector Selector Spring Detent Selector Bolt Catch Bolt Catch Spring (not for 9mm/40sw/45acp use) Bolt Catch Button Bolt Catch Roll Pin (not for 9mm/40sw/45acp use) Front Pivot Pin Rear Take Down Pin Take Down Detent (2) Take Down Detent Spring (2) Magazine Catch Spring Magazine Catch Button Magazine Catch Triggerguard Triggerguard roll pin Buffer Retainer Pin Buffer Retainer Spring