The Accu-Wedge will improve fit and eliminate the wobble between the upper and lower of your AR15/M4/M16 type rifle. This drop-in parts helps promote improved accuracy and allows the user to shoot tighter groups. The small wedge-shaped part is molded of high-density thermoplastic rubber and is easily installed in the lower receiver beneath the rear take-down pin. The quickest, easiest, and least expensive accuracy-upgrade you’ll ever find for your AR15!