1/2" End Mill Cutter Adapter Holder Bridgeport R8 Shank Adaptor Milling Cutting 1/2" End Mill Adapter Bore: 1/2" ; 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: 0.95 lbs