The step drill bit are made of high speed steel, strong and durable. X-shape cutting blades design enables a faster and smoother cutting. 1/4 "or 3/8" rods are compatible with most electric drilling tools, suitable for Home DIY, and General Building/Engineering Use. fit for drilling holes in stainless steel sheet, aluminum alloy, plastic material and wood(the board must be smaller in thickness than the height of step drill bits, thickness not exceed 0.12 inch/3mm). Step Drill Bit Size: #1: 1/4" to 1-3/8" 10 steps (1/4'', 3/8", 1/2", 5/8", 3/4", 7/8", 1", 1-1/8", 1-1/4", 1-3/8") #2: 3/16" to 7/8" 12 steps (3/16'', 1/4", 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4", 13/16", 7/8") #3: 1/4" to 3/4'' 9 steps (1/4'', 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4") #4: 1/8" to 1/2" 13 steps (1/8", 5/32", 3/16'', 7/32", 1/4'', 9/32", 5/16", 11/32", 3/8'', 13/32", 7/16'', 15/32", 1/2'') #5: 3/16" to 1/2" 6 steps (3/16'', 1/4'', 5/16", 3/8'', 7/16'', 1/2'') Package list: 5 x Step drill bit 1 x Automatic center punch 1 x Storage box