Complete Premium Billet Carbine Lower Receiver comes standard with a Lower Parts Kit, that utilizes no MIM parts, and a Premium AIMSURPLUS Ambidextrous Safety Selector. They feature a patented, proprietary Last Round Bolt Hold Open, the best on the market. It also comes standard with AimSurplus SSTAT LE Trigger, an AimSurplus Ambidextrous Safety, Stainless Steel .308 Carbine recoil Spring and 6.5 oz heavy buffer standard.