Premium 5% Cobalt Steel ,68 HRC (Rockwell Hardness Scale) ,the Cobalt Usually Give the Best Heat,Wear and Chip Resistance and Long Tool Life. The Cutting Edge has been Ground Three Times and is made of Cobalt Steel, which has High Hardness and Heat Resistance. It is Designed for Drilling through Stainless Steel, Hardened Steel, Iron, Aluminum, Pipes, Wood, PVC, and Plastics. This Heavy Duty Work Cobalt Drill Bit is Typically Capable of Running Two to Three Times Faster.Despite the Higher Price,the Cost Per Hole When Using Cobalt Drill Bit Will be the Lowest,Since It Can Produce So Many More Holes. The Sufficiently Sharp Bit Edge Can Cut the Metal Material into Long Strips of Iron Chips rather than Slowly Grinding Through the Material with a Blunt Drill Bit. 17Pcs 135 Degree Cobalt Industrial Hss Drill Bits Kit Includes :1/16 (2pcs), 5/64, 3/32 (2pcs), 7/64, 1/8 (2pcs), 9/64, 5/32, 3/16, 7/32, 1/4 (2pcs), 5/16, 3/8, 1/2 . B09MRW8399