For making holes in thin sheet metals.Titanium-nitride (TIN) coated step drill with a surface hardness that makes the tool last 4 to 5 times longer than ordinary step drill bits.Same surface reduces friction, resulting in a tool that runs cooler and effective, self-lubricates while running dry.Self-centering point.Drills holes from 4 mm to 22 mm in 2 mm increments.Shank 3/8" (10 mm)