... shank short twist drill GB/T613.2-96 D6~D40 Hss Step drills from 4-39 mm. Coated with a TIN ... 18, 21, 24, 27, 30, 33, 36, 39 etc.The Hss step drills are perfectly round holes in steel, brass, copper ... up to 1/2" holes sizes with one bit. Ideal tool for sheet metal workers, electrical contractor, auto mechanics, and general ... slipping in drill chuck or bit extension. high precision Hss 2 step drills