Item Type: Spiral Step Drill Bit Material: High Speed Steel Containing Cobalt Purpose: Spiral Step Drill Shank Type: Hex Shank Shank Diameter: 1/4in Drilling Diameter: Approx. 4-12mm / 0.16-0.47in 1M35 Grade Cobalt Steel: Made of strong M35 grade cobalt steel, with 5% cobalt added to form a hardened heat resistant alloy with longer life 29 Size Ranges: With 9 size ranges from 4mm to 12mm, you can use one to drill up to 9 holes of different diameters, saving your time and effort to replace the 3Application: Very suitable for drilling new holes or expanding existing holes on stainless steel, and softer metals such as iron, brass, copper, aluminum, etc. 4Greater Torsion: This 1/4in hex shank can be clamped tighter by compatible s and screwdrivers to achieve greater torsion 5Smooth Chip Removal: This is a M35 cobalt containing step drill, which can open holes quickly, cut faster, and remove chips smoothly.1 x Spiral Step Drill Bit