The trigger guard lips on the AR-15 lower are the weakest item on the receiver. When installing or removing the roll pin, they can easily be snapped or fractured. The Trigger Gunner's Puck fits the circular cutout on the Gunner's Mount. The Gunner's Puck fits most mil-spec lower receivers, with cutouts for the bolt stop, safety/selector, magazine release, and magazine well. Trigger Gunner's Puck will fit the circular cut on the Gunners Mount or is good for standalone use. Puck cut to have the lower receiver fit by way of the grip portion when grip removed, most Mil Spec lowers. It will accommodate the bolt stop. Safety/Selector Mfg: Present Arms Inc SPECS: Fits mil-spec AR-15 lower receivers.