Surefire Shim Kit, SF3P / SFMB / Warcomp-556, 1/2-28. Made of quality stainless steel, this shim kit assembled by Surefire is an ideal 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 12 shims of various thickness to allow you to accurately install muzzle devices to your firearm.