Purpose: Use the center point to fix the solder joint and press it down (there is a spring device on the back of the nail to expand and contract) When the serration touches the solder joint surface, it can be rotated with the power tool to remove the solder joint Set contains: The 9-piece drill bit includes a twist drill, an electric welding drill, two welding drill bits and 4 serrated sets Multi-function: The drill bit with approximately 3 inches hexagon shank is for the standard quick-change serration sleeve, thus providing the versatility required for drilling : Drill bits and welding drills are high-speed steel, which can quickly drill holes and remove metal materials from solder joints : The special tip design provides when drilling the surface, Manufacturer: LORYEANM