Precision ground metric drill bits made from M42 high speed steel bars with 8% cobalt achieving a hardness of some 63.5 - 65 Rockwell. The Cobalt allows the drill bits to hold their hardness at higher temperatures. Intended for use on alloy and hardened steels, cast iron, titanium and many other really tough, hard-to-drill, materials such as stainless steel. Perfect for home and production use. Available in a range of metric sizes. It is advisable to use coolant when appropriate.