【M35 Cobalt Superhard High Speed Steel】: ISI M35/1.3243/SKH55/M35 steel is a kind of high speed steel containing cobalt, which has the characteristics of high wear resistance, high pressure resistance and sintering resistance. Ideal for steel and plastic drilling with high-speed cordless drills. 【100 extra-long warranty period】：If you have any questions about the product, please contact us and we will answer you within 12 hours. If the hexagonal handle breaks, refund or replace for 100% . 【Unibit step drill bit compatibility 】：Unibit step drill bit can quickly and smoothly drill holes of different diameters, such as stainless steel, aluminum, wood, plastic board (the board must be thinner than the height of the step drill). 【M35 four spiral groove】: Step drill bit for metal four cutting blade design. Faster, smoother cutting and easier separation of sawdust.The service life is twice that of ordinary ladder drills, the drilling accuracy is significantly improved, the cutting speed is faster when drilling, and it has a unique effect on stainless steel drilling. 【Common sizes】: Step bit contain sizes from 1/4” to 1-1/8” ,Common sizes 7/8”, 1-1/8” minimum size 1/4, maximum size 1-1/8”, total 15 sizes： 1/4 "-1-1/8": 1/4", 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4", 13/16", 7/8", 15/16", 1", 1-1/16", 1-1/8". 【TiAlN】:TiAlN coating is a new coating material in recent two years.ndustrial-grade construction ensures durability and longevity It has high hardness, high oxidation temperature, good thermal hardness, strong adhesion, low friction coefficient and low thermal conductivity coefficient. Four Spiral Flute M35 Step Drill Bit Set 1/4" - 1-1/8”(15 Sizes), 3/8" Shank for Metal Step Drill bit, Impact Resistant Cobalt Step Drill Bit, for Stainless Steel, Wood, Aluminum, Plastic