High Cutting Performance Long Lasting. Used to bore holes in mild steel, aluminum, stainless steel, etc. Speedy Effortless Tool - Easily Cuts through hard metals such as stainless steel and cast iron, although they can be used for softer materials, too. Extremely heat resistant; must be used and operated at 1500 RPM or greater for maximum efficiency. Extremely Durable-Lasts Longer, Hardened alloy, measuring hardness up to 67, for much faster cutting and extra longer life span, with up to six times when compared with an average HSS drill bit.