Cle-Line C10629Cleveland M42 cobalt heavy duty jobber length drill bit set. Cobalt steel tools are similar to high-speed steel, but with more cobalt for improved performance when cutting harder metals such as stainless steel or nickel alloys. Gold oxide is a thinner oxide surface treatment than black oxide typically used to identify cobalt steel tools; performance is similar to uncoated tools. High red hardness for extended wear life in high heat conditions. Applicable for aluminum, copper alloys, inconel, titanium alloys, tool steel, die steel