3/8" End Mill Holder Adaptor Tool R8 Shank Bridgeport Milling Cutting Adaptor 3/8'' end mill adapter Bore: 3/8"; Drawbar Thread: 7/16"-20 Hardened and Ground ; Made for high quality steel forgings Precision ground concentric ; Ground shank and hole, heat treated for double accuracy Quantity: 1; Weight: .95 lbs