Hardened steel shims ensure precise fit and correct alignment of flash suppressors, muzzle brakes, and compensators. Large (thick) shim allows 90Adeg of rotation and can be used as a spacer for barrels not having a relief cut behind the threads. Medium shims add approximately 45Adeg of rotation. Small shims used with large and medium shims provide smaller degrees of rotation for finely-tuned, critical alignment. Mfg: Primary Weapons