The Spike's Tactical ST-15 Multi. Cal. AR Lower Receiver Group is the standard Rifle lower that all ST-15 Rifles are assembled with. The selector markings are bullet pictograms. Low Shelf, RDIAS Compatible ST Standard LPK 6-Position Buffer Tube, Castle Nut, Staked Latch Plate 17-7 Stainless Buffer Spring ST-T2 Buffer SB Tactical Brace Magpul MOE Pistol Grip Yankee Hill Machine handstop Rise Armament QD installed on handguard CMMG ambi charging handle