HSS step drills: high-performance high-speed steel. Through the heat treatment and tempering, firm and wear-resistant. The surface of the drill is coated with anti-rust oil to prevent rusting. The step drill stays sharp Size: 4-12mm / 4-20mm / 4-32mm. Various sizes, free control over the size of the holeDesign: The hex shank to avoid slipping in the drill chuck. The step drill suitable for hand drill, pillar drill and electric screwdriver HSS 6542 Twist Drill: Equipped with a HSS 6542 twist drill for positioning to reduce the damage of the step drill. Rotate the drill in a circular motion without much pressure and the drilling speed is fast Usage: Perfect for home DIY and general engineering use. The step drill can be used for many different materials such as steel, brass, wood, plastic, aluminium, insulation boards, copper, fiberglass and PVC. Only for ordinary aluminum, iron and steel plate (thickness not more than 4mm, hardness less than 25HRC), not for stainless steel