Size: Size 1: length 7 cm, meter (mm): from 4 to 12: 4,5,6,7,8,9,10,11,12 Size 2: length 7 cm, meter (mm): from 4 to 20: 4,6,8,10,12,14,16,18,20 Size 3: length 10 cm, meter (mm): from 4 to 32: 4,6,8,10,12,14,16,18,20,22,24,26,28,30,32. With 4mm Twist Drill: The 4mm twist drill can pre-drill the step drill, which makes the step drill less easily damaged than the Ordinary step drill bit. Material: Step drill bits are suitable for DIY, home and construction. It is very suitable for drilling holes in a variety of materials such as steel, brass, wood, plastic, thin iron plates, aluminum materials, insulation plates, PVC plates, etc. Only suitable for ordinary aluminum, iron and steel plates (thickness cannot exceed 4 mm, hardness is less than 25HRC), not for stainless steel. Sturdy and durable: 3-piece step drill bit set is made of high-quality HSS steel and coated with titanium to reduce friction and heat. Attention: If you have any questions about the quality of our 3PCS Step Drill Bits,