Treated by Nitrogen to increase the hardness and abrasion resistance. Automatically deburr holes as you drill. Made of high speed steel, 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 bag Color: gold Product material: steel Product handle: diameter 10mm, round handle Product length: about 98mm Package Contents: 2 x 4-42mm HSS Step Cone Drill Bit Only the above package content, other products are not included. Note: Light reflection 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.