Treated by nitrogen to increase hardness and abrasion resistance. Automatically deburrs holes as you drill. Made of high-speed steel for durability and long life. Includes 14 sizes: 4, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42mm. Suitable for workpieces with hardness up to 25 HRC. Ideal for drilling holes in various materials such as steel, wood, thin iron, aluminum alloy, insulation boards, and PVC sheets. Product specifications: 4-42mm (14 steps: 4-6-9-12-15-18-21-24-27-30-33-36-39-42mm). Packaging: OPP bag. Color: gold. Material: steel. Handle: 10mm diameter round handle. Length: approximately 98mm. Package contents: 1 x 4-42mm HSS step cone drill bit. The package includes only the items listed above; others are not included. Note: Lighting and display differences may cause slight variations in color between the image and the actual item. Measurement may vary by +/- 1-3cm.