Cobalt drill bits were constructed and designed to be able to drill particularly hard exteriors such as cast irons, titanium or treated stainless steels. Cobalt drill bits were made from a solid composition of steel and cobalt. It is made to withstand high speeds and is designed to last long. There are two grades available for cobalt drill bits, these grades mirror the amount of cobalt contained within the high-speed steel drill bit. For example, an M42 grade cobalt drill bit contains 95% high-speed steel and 5% cobalt, if the concentration of cobalt is too high then the cobalt drill bit will become brittle and will not be able to withstand high-speeds. Keep in mind that the harder the drill bit, the more brittle it is. A cobalt drill bit is heat-treated to change its color from steel blue to a shiny gold, this helps distinguish it from other standard drill bits.