This Irwin Unibit Step Drill 3-Piece Pro Kit combines many common bit sizes. Pieces are made of high-speed steel (HSS) which withstands heavy usage without any loss of control, and all of them have starter tips to eliminate center punches. Step drill bit set features straight flutes that protect thin materials. Each of the pieces has markings engraved onto the sides, which show the exact measurements for each step, and the specialized tips help maintain position when starting to drill, so nothing slips when pressure is added. Irwin drill bit set pieces have three-sided shanks that eliminate vibrations. Bit Sizes: #1 (1/8 In. to 1/2 In. 1/32 In. steps), #2 (3/16 In. to 1/2 In. 1/16 In. steps), #3 (1/4 In. to 3/4 In. 1/16 In. steps)