Material: High Speed Steel 4241 (Suitable For Workpieces With Hardness Below 25 Degrees) Cutting Material: Thin Iron Plate, Aluminum Material, Insulating Board, PVC Board Wood ( The Recommended Thickness Is Within 5mm) Features: 5 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 1. This Is A New Type Of HSS 4241 Steel Large Step Taper Drill Cobalt Coated To Reduce Friction And Run Cooler 2. Cobalt Steel With Titanium Coating Ensures The Bits Have Exceptional Durability And Will Stay Sharp For Many Years. 3. It Is Very Suitable For Cutting Holes In Various Materials, Including Carbon Steel, Brass, Wood, Plastic, Etc. 4.The Bits Come Supplied In An Organized Aluminum Case For Easy Storage And Transport. 5This Set Is A Must-have For HVAC Professionals And DIY Enthusiasts. Notice: 1. 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) 2. During Drilling Operation, Water Is Injected While Drilling To Cool Down, Which Effectively Prolongs The Service Life Of The Drill. (Recommended Speed 250~400)