1. Wearresistant and durable drill bits 2. For the operation of hand drill (above 550W), the thickness is 1 2mm, and the hole diameter is greater than 14mm, a bench drill is required. (It is recommended to drill the workpiece with a stainless steel hardness below 25 degrees) 3. During drilling operation, water is injected while drilling to cool down, which effectively prolongs the life of the drill. (Recommended speed 250400) 4. This is a type of HSS 4241 steel large step taper drill cobalt coated to reduce friction and run cooler. 6 piece step drill bits set replaces 50 individual drill bits which saves you a lot of trouble and space. Two flute design gives you faster, smoother cutting. Large bit has 3 sided shank and small bits have hex shank to prevent slip in drill chuck 5. Cobalt steel with titanium coating ensures the bits have exceptional durability and will stay sharp for many years.