The SLR Rifleworks Multi Position AR-15. AR-10, LR-308 Barrel Dimple Drilling Jig features 5 spacings for blocks with .400" .425" .450" .470" and .500" center to center. The 5 position flats for Vice mounted drilling help to keep barrel stable. FeaturesDimpling Jig for .750" BarrelsIncludes Jig , Hardened Centering Screw and Custom Hardened Drill bushing5/32" drill bit requiredBlack Hard Coat anodized Drill bit and Allen Wrenches available separately Note:Numbers on Jig face the front (towards muzzle) Spacing to be used goes on DIMPLE side with drill bushing (opposite gas port)If using one dimple only, always dimple under gas port