Bits in the 29-piece cobalt M35 a hard, heat and wear-resistant metal. It an ideal material for drilling very hard and abrasive metals such as stainless or high-alloy steel and cast iron. Each bit in the Irwin cobalt drill bit set has a 135-degree split point that starts quickly and won't walk across work surfaces. Bits larger than 3/8 of an inch have a reduced shank so you can use them with 3/8 in. drill chucks. 29-piece drill bit set includes a metal case with a rubberized shell, removable bit cartridges and a tap and die selection chart.