Aero's Gen 2 stripped lower receiver is the perfect base for your custom AR-15 build. Machined to mil-spec dimensions, this lower works with standard AR-15 components and ensure the highest quality with a correct component interface. Gen 2 improvements include nylon tipped tensioning set screw to fine tune the fit of the upper and lower receiver, and an increased magwell flare easier insertion of magazines and a sleeker look. The rear takedown pin detent hole is threaded for a 4-40 set screw. This lower is made in America, machined from 7075-T6 forged aluminum, marked "Cal Multi".