Step Drill Bit Material: M35(HSS4241,HSS4341,M2 are available) Step Drill Bit Style: Spiral Flute(Straight Flute is available) Step Drill Bit Shank: 3-Way Clamping (Hex Shank Size 1/4" Inch (6.35 mm),Cylindrical Shank are available) Step Drill Bit Surface: 1