AAC's Barrel Shim Kit includes 6 different shims of varying thicknesses for the purpose of properly timing a flash hider or muzzle brake on a particular barrel, offering a far greater degree of precision than that of any crush or peel washer while also being faster and less labor intensive to install correctly. Each shim is color coded according to its thickness, and multiple shims may be combined and used together if necessary in order to acquire the exact thickness required for proper muzzle device orientation.