New Frontier Armory C-4 stripped billet lower receiver for the AR-15 marked multi-cal for your building choice. This is machined from 7075 T6 aircraft grade aluminum.Other features include: Machined and engraved to be compatible with 45 and 60 degree short throw fire control selectors such as the BAD_ASS ST 45 Lever. Take down pin spring and detent hole is threaded for a 4-40 set screw for easy capturing (hardware included). The Upper tension screw behind grip screw (threaded hole with hardware included) to adjust any “slop” out of vertical fit between upper and lower. Ambidextrous trigger finger rests with grooves (above and below mag release / mag catch). Compatible with Norgon and other aftermarket ambidextrous mag releases.Threaded bolt catch pin (Threaded hole and hardware). Integrated large opening “winter” trigger guard. Manufactured to MILSPEC on state of the art CNC equipment for consistent quality parts and exacting tolerances.