CO-Z 5pcs Hss Cobalt Multiple Hole 50 Sizes Step Drill Bit Set with Aluminum Case Cobalt high speed steel along with the titanium coating ensures extreme durability, will stay new and shiny for years to come. Different sized shanks ensure compatibility with 1/4, 3/8 and 1/2 in. chuck sizes. Non-walking drill tip provides fast and smooth drills on steel sheets, aluminum sheets, wood board, plastic board etc. (the board must be smaller in thickness than the height of step drill bits). Please mark the spot that you are to drill for easier drilling and improved drill bits life. All the bits come in a well-organized case for easy transport and storage.