1. These drill bits are made from high-speed steel for high hardness and durability, Sturdy and having long service time.2. The twist design is adopted to center the tool tip and improve the cutting accuracy.   Prevents the bit from displacement during work, and removes debris and particles more easily.3. Long drill bits can be used for drilling into metal, wood, plastic, PVC. First use a common drill to drill holes, and then use an extended drill to pass through the holes.4. Note that the speed should not be too high to avoid breaking the drill.