1.00 mm Cutter Diameter x 3.00 mm Length of Cut Carbide Square End Mill For Hardened Steels Up to 55 HRc, 5 Flutes, AlTiN Nano Coated. Designed to mill hardened tool, die, and mold steels up to 55Rc, this Harvey Tool offering of End Mills for Hardened Steels - Square - For Steels Up to 55Rc features tooling with 5 flutes and the latest generation AlTiN Nano coating for superior hardness and heat resistance.