We stock a range of drill bits for gunsmithing and other precision engineering jobs. High Speed Steel (HSS) drill bits are suitable for drilling aluminium and other soft metals. To successfully drill hard metals like stainless steel and cast iron, drill bits ideally should be Cobalt or Titanium coated. Cobalt bits are not coated, they are made from solid cobalt steel. The more the cobalt, the harder the steel. A minimum of 5% Cobalt should be used to achieve M35 class Cobalt steel. This has a Rockwell C hardness rating of 65.5 to 67. Titanium Coating is much harder at 82 Rockwell C, but because the titanium is just a surface coating, if the drill bit is sharpened the hardness of the bit will reduce.