Compatible with Stainless Steel: Great for drilling iron plates, aluminum plates, stainless steel, vinyl, wood, resin, etc., enlarging the lower hole, beveling, household DIY, deburring, etc. HSS-Co M35 Steel: HRC89 hardness step drill has a high hardness surface with titanium nitride coating. Sharpens better than ordinary steel step drills. Reduces heat produced during friction. 【Industrial Grade Coating】TiAIN Titanium Nitride coating with a surface hardness up to 89 degrees, so it can withstand loads on high speed rotations. Ideal for high-speed drilling: The A1203 forms a hard protective layer when drilling, improving the resistance of high temperature and grinding resistance. [Range of application] Popular for its high stability and long life. The holes are expanded in order to allow for multiple sizes and enlargement corrections. In addition, the shape of the shaft is hexagonal shaft, so it can be used with impact drivers, electric drills, charging drills, etc. Set of 2: 4-12 mm (9 Tiers) (4,5,6,7,8,9,10,11,12). 4-20mm<9 Tier> (4,6,8,10,12,14,16,18,20) Includes a step drill storage case.