Unibit Step Drill Bit, Cobalt HSS, 9/16" to 1", 8 Hole Sizes, 1/2" Shank IRWIN Unibit Cobalt is made of high speed steel, this step drill bit will last longer in the toughest of materials. Best suited for maintenance and repair work. 6X Longer life vs. the competition. M35 grade Cobalt HSS. Radial concave flute. 3-Flatted shank. Speedpoint tip. Laser marked sizes.