This is a professional drill bit set. It includes drill bits with diameters of 2.5cm, 3.3cm, 4.3cm, 5.4cm, 6.8cm, 8.6cm, each size comes with 1 piece. Industrial grade high-speed steel for better durability and sturdiness. Suitable for drilling in tough material, including aluminium, cast iron, brass, copper, magnesium alloy, plastics, etc. Feature - Color: Yellow - Material: Stainless steel - Bit diameter: 2.5cm, 3.3cm, 4.3cm, 5.4cm, 6.8cm, 8.6cm; Length: 5.8cm - High-speed steel with coating treatment, tougher and more abrasion resistant for longer working life and high work efficiency. - design drill bits, accurate and fine, increase drilling speed. - Mainly for drilling wood, plastic, fiberglass, printed circuit board, and metal including copper, aluminum, tool steel, cast iron, and heavy-duty abrasive alloy metal, etc. - for home DIY, building and engineering use etc.