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.