At APM we are proud to offer high quality American made billet AR-15 80% lower receivers that meet or exceed mil-spec standards. All of our 80% lowers are made of the highest quality 6061-T6 domestic billet aluminum. They also have features like; threaded bolt catch pin (included) and can also accept standard mil-spec roll pin if you desire, the rear take down detent spring hole is also threaded to accept a #4-40 set screw (included), and all lowers have also been drilled and tapped to accept a 1/4″-28 set screw (not included) to adjust for tension on your upper.