... following size:Sizes: 4-12 mm step: 4, 6, 8, 10, 12 mm 40-20 mm step: 4, 6, 8, 10, ... 12, 14, 16, 18, 20 mm 5-28 mm step: 5; 8.8, 11.8, 15.3, 19 ... 5, 28 mm 40-30 mm step: 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, ... 30 mm 4-39 mm step: 4, 6, 9, 12, 15 ... 24, 27, 30, 33, 36, 39 etc.The Hss step drills are perfectly round holes in steel, brass, copper, ...