set of 3 HSS6542 M2 Steel Spiral Groove Step Drill Bit Set for Stainless Steel Metal Wood Hole Suit for use in hardness under 28 artifacts,(Such as: Stainless steel , iron plate, aluminum, wood ) You can use water to cooling it when it is work and it can be used for even longer 4mm to 32mm 15 Steps (4mm,6mm,8mm,10mm,12mm,14mm,16mm,18mm,20mm,22mm,24mm,26mm,28mm,30mm,32mm) 4mm to 12mm 9 Steps (4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm) 4mm to 20mm 9 Steps (4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm,18mm,20mm)