Metric drill bits made from M42 high speed steel bars with 8% cobalt. 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 3.0, 4.0, 4.5 and 5.0mm.