3pc HSS 4-12/20/32mm Spiral Groove Step Drill Bit Set - Golden Specific Feature and Material: HSS Metric Spiral Flute Step Drill Bits, Titanium Coated Spiral Flute design, better for faster drilling, prevent slippage when in chuck Shank diameter: 10mm(0.39'') for 4-32; 8mm(0.31'') for 4-20; 6mm(1/4'') for 4-12 Titanium nitride coating runs cooler and lasts longer Hole Cutter step included: 4-12/20/32mm