Treated by Nitrogen to increase the hardness and abrasion resistance.Automatically deburr holes as you drill.Made of high speed steel, durable and long lasting.14 sizes, 4-42mm(4, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42mm)suitable for workpieces with hardness below 25, Widely used to cut holes in a variety of material like steel, wood, thin iron, aluminum alloy, insulation boards, PVC sheet, .Product specifications: 4-42 (14 steps: 4-6-9-12-15-18-21-24-27-30-33-36-39-42mm)Product packaging: OPP bagColor: goldProduct material: steelProduct handle: diameter 10mm, round handleProduct length: about 98mmPackage Contents:1 * 4-42mm HSS Step Cone Drill BitOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.