IRWIN HSS Cobalt Drill Bits are perfect for drilling stainless steel and other high alloys. Their 135 split point grinding ensures perfect centring and reduced drilling pressure. An industrial quality ground flute ensures high accuracy drilling and fast removal of chips. The drill bit body is manufactured from high-quality HSS steel containing 5% cobalt (Co). The added 5% cobalt improves the red hardness (heat resistance) of the drill bit and results in significantly extended life. It has an attractive golden tempered surface finish. This 15 Piece Set contains the following sizes 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 8, 9, 10mm.