6-60mm HSS 4241 Spiral Groove Step Drill Bit Unique ladder structure , it can open multiple Aperture it can not easily be broken. It can deburr, chamfer and open hole, but ordinary twist drill can't 6-60mm(12 steps:6,10,15,20,25,30,35,40,45,50,55,60mm) Shank Diameter: 13mm.Material: HSS 4241