Overview This Rugged shim set is comprised of 3 different sized shims 1 large, 8 medium, and 1 small. The large shim can be used to give the installer one half of a rotation or as a spacer for barrels that do not have relief cuts behind the threads. Shim 2 is used in varying quantities to achieve the proper alignment of your muzzle device. This shim gives the installer approximately 45 degrees of rotation. If needed, Shim 3 can be used where smaller degrees of rotation are needed for proper alignment.