Features Collet Chucks TIR: <.0001 at collet face Made from nickel chrome molybdenum alloy, hardened to 55 - 58 Rc. Ground surface for perpendicular contact between retention knob and holder. AT3 or better taper contact: .0028 °s; tolerance variation 80 to 126 millionths Drive keys milled to same depth for symmetrical body design. Body is equal in diameter to the size of the nut for greater rigidity and also prevents chips from packing in or wrapping about. ER Ball Bearing Nuts (Installed) Ground collet face. Smooth to prevent coolant flare and provide better balance. Provide 50% more gripping power than standard nuts.