CMD232541 HSS Step Drill Bit 4mm x 12mm. High speed molybdenum steel step drill bit for rapid drilling and deburring in sheet materials up to 3 mm thick. The cone shape unique design of the RS PRO step drill bit allows various popular hole sizes to be drilled with just one tool. This drill bit eliminates vibration and chatter and provides clear holes in applications requiring small hole size increments in stainless steel, aluminium and plastic.