Perfect Step Drill Bits suitable for drill holes in various material within 3mm/0.12 inch (Iron Plate, Copper Plate, Aluminum Plate); within 5mm/0.2 inch (Wood, PVC sheet, Insulation Boards). Not suitable for hard and brittle materials such as stainless steel, glass, tile floors, walls etc.HSS combined with a titanium coating. More capable and durable.Hex Shank fits into all power tools more easily and securely, especially for locking into quick change chuck. It is better clamped on the pistol drill to prevent slippage and shedding during the rotation.Bit #1 (5 steps): 4-12mm (4mm, 6mm, 8mm, 10mm, 12mm); Bit #2 (9 steps): 4-20mm (4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm); Bit #3 (15 steps): 4-32mm (4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm, 22mm, 24mm, 26mm, 28mm,30mm,32mm) ;1 Automatic Spring Loaded Center Punch Power Tools