Made of high speed steel construction for proven capability and durability. Twist design increases cutting speed with self-centering and prevents walking, clears chips and particles faster. Suitable for drilling stainless steel, ordinary steel, angle iron, aluminum, copper, wood, and other materials. Ideal for precise drilling, electronic assembling, tool making, model making, jewelry engraving, and hobbies. Set includes: 21mm, 22mm, 23mm, 24mm, 25mm, 26mm, 27mm, 28mm. Material: High speed steel. Size Chart: 21mm (0.83 inch), 22mm (0.87 inch), 23mm (0.91 inch), 24mm (0.94 inch), 25mm (0.98 inch), 26mm (1.02 inch), 27mm (1.06 inch), 28mm (1.10 inch). Package Includes: 1 Piece Twist Drill Bit