Features: Sharp and durable, accurate positioning, cutting edge clear.Each bit has a double end and grinding at a standard 60 degree angle. Quick cutting speed, and good chip removal for precise center drilling in metals.Used for all kinds of materials. can be applicable to metal, alloy, iron, steel, copper, aluminum and other processing. A center drill bit is a very useful pieced of kit if you are doing any metal working. They are incredibly accurate, solid and useful.60-degree angle plain center drill bits are used for drilling precise center holes with diameters range from 1mm to 5mm. They also can give you an extremely good starter holes and you can drill up with the correct size drill bit and then tap it. Name: Center Drill Bit Set Material: High Speed Steel ( HSS ) Size: 1.0 1.5 2.0 2.5 3.0 4.0 5.0 (mm) Tips in using center drill bits : 1. Fix the work piece deep in the Lathe machine to prevent wobbling when rotate 2. Get rid of acid surface before drilling and use oil or proper lubricant to protect the bits 3. A good rule to follow is to go 2/3 deep on the tapered section 4. Stop immediately if the drilling sound is abnormal and fix any problem before resuming 5. Clean the center drill bits before and after drilling, and apply oil to store it properly. stored in a solid storage case. Number 1 and Number 4 are the two most common sizes.