When you want to start your AR build, the Cornerstone lower is the starting point. It is machined from forged 7075-T6 aluminum to tighter than Mil-Spec tolerance with nylon tipped tensioning screw to ensure the solid fit between upper and lower. It features a flared mag well, pictogram safe and fire indicators, chevrons on the front of the mag well, and the distinctive Grey Ghost markings. The lower functions with nearly all available AR parts kits and uppers.