These are the highest quality spot weld drill bits Ė Titanium and Carbon Nitrited coated. The bitís purple color comes from the carbon nitriting process, which makes this bit last 10 times longer than the standard HSS bit . Rockwell Hardness of 96, max temp rating 1600 degrees. With this temp rating you can use the MAX2U bit dry or with cutting oil. This bit is available in 8mm diameter.