... following tandard straight shank short twist drill GB/T613.2-96 D6~D40 Hss Step drills from 4- ... , 10, 12, 14, 16, 18, 20 mm 5-28 mm step: 5; 8.8, 11.8, 15.3, 19, 24 ... .5, 28 mm 40-30 mm step: 4, 6, ... copper, aluminum, wood and plastic. Drills up to 1/2" holes sizes with one bit. Ideal tool for sheet ... prevents slipping in drill chuck or bit extension. high precision Hss 2 step drills