The EZ Aim Gong Hanger with Recoil Spring is designed to be mounted on the top of a 2 x 4. It fits most steel targets. The targets are best mounted with a center bolt hole. The recoil spring reduces the impact of the projectiles on the AR500 steel target by absorbing some of the energy. Attaches to the 2 x 4 lumber with a steel wedge that creates tension on the wood. Bolts and hardware are supplied to permanently mount it to the wood.