Precision-formed carbon steel shims take up the gap and center the bolt body after truing the receiver with the .715'''' Bolt-Way Reamer. Saves time and effort by eliminating the need to fabricate shims from scratch. To install, undercut the bolt body to accept the shims and solder or adhere them in place with the included retaining compound. Front and rear two-piece shims are manufactured to precise tolerances and pre-contoured to ensure a perfect fit on any .700'''' diameter bolt body. After installation, machine shims to .7135''''-.7145'''' O.D. to provide proper clearance for snug bolt fit and ensure reliable cycling. Mfg: Brownells SPECS: Carbon steel, polished finish. Front Shims - Nominal .400" (10.2mm) wide x .012" (.305mm) thick. Rear Shims - Nominal .700" (17.8mm) x .012" thick. Includes front and rear shims, retaining compound, and complete instructions.