Quality Material:HSS high speed steel with titanium coating for strength and longevity. Coated by titanium,this step drill set performs well in heat,corrosion and rust resistance.Package: 4-Piece HSS Groove Step Drill Bit (4-12/ 4-20/ 4-32mm ) + 1 Automatic Center Punch.Titanium Coating: The cone drill bits are made by high speed steel, strong and durable. The titanium coating resists the drill bits from corrosion and rust, deduces friction making it easily to do multiple drills on surfaces such as thin iron, wood, plastic board, composite board, not suitable for drill stainless steel or any other harder metal.Easy Drilling:Two-fluted design provides faster, smoother cutting, provided with small pressure and the sets. Stepped grooves prevent slippage in the chuck. Various Specifications:The titanium coated step drill bit set has 28 different apertures. They can process different kinds of diameter holes, which greatly saves you a lot of trouble.