The KleenBore Accu-Wedge buffers the AR-15/M16/M4 bolt carrier to reduce wear and tighten the connection between the upper and lower receivers. The Acu-Wedge simply installs with no gunsmithing required underneath the AR-15/M16/M4 rear takedown pin, reducing or more likely completely eliminating upper to lower fitment slop”! Put some quality feel into your wobbly AR with the Accu-Wedge.