Surefire Shim Kit, 1/2-28. Constructed of stainless steel, this shim kit from Surefire is a great solution to properly index your muzzle device. Designed with an outer diameter of .700 & and inner diameter of .510, this kit works with 1/2 x 28 TPI threaded barrels chambered in .22 caliber, 5.56mm or 9mm. Along with a tube of Rocksett in this kit, it also features 9 shims of various thickness to allow you to accurately install muzzle devices to your firearm.