- Klutch Cobalt Step Drill Bit Set - 3/16in. to 1 3/8in. Dia, 5-Pc. Set High-speed, heavy-duty steel with cobalt coating Professional quality 3/16-1/2in. dia., 6-step bit 1/4-3/4in. dia., 9-step bit 1/4-1 3/8in. dia., 11-step bit