• 3-piece stepped drill bit sheet metal drilling set 3-piece stepped bit 3-piece stepped drill bit set made of high speed steel. Cutting without cracking with double groove system. 1st drill : 4, 6, 8, 10, 12 mm 2nd drill : 4, 6, 8, 10, 12, 14, 16, 18, 20 mm 3rd drill : 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32 mm Tin plating 6 times more durable than normal hss inserts.