Surefire Shim Kit, 5/8-24. This kit contains quality stainless steel shims assembled by Surefire. Use this kit to properly index your muzzle device. Designed with an outer diameter of .770 & and inner diameter of .635, this kit works with 5/8 x 24 TPI threaded barrels chambered in .30 caliber, 7.62mm or .300 Blackout. Along with a tube of Rocksett in this kit, it also features 8 shims of various thickness to allow you to accurately install muzzle devices to your firearm.