The STS (Short Throw Safety) AR-15 Stripped Lower Receiver is the perfect lower to start your build. Custom designed markings accept short-throw safety selectors while maintaining mil-spec dimensions and correct component interface. Selector markings will work with 45, 60 or 90 degree safety selectors. STS lowers are marked and milled to accept short-throw safety selectors, but will work with standard selectors as well. Rear take-down pin detent hole is threaded for a 4-40 set screw. Works with standard AR-15 components and magazines. Made in the USA. NOTE: Requires a lower parts kit, buffer & stock of your choosing to complete.