If you've been around tools for very long you've probably run into a situation where the head of a screw has become stripped or the head of a bold has broken off, preventing you from extracting it in the normal way. Fortunately there is still a way for you to get a damaged screw or bolt out of wood or metal. It is called a screw extractor. A screw extractor fits on your variable-speed electric drill. It looks somewhat like a drill bit, although it tapers up from a point like an inverse pyramid and the ribs on the bit are not designed to drill out wood or metal, but rather to grab hold.
Put a metal drill bit in your variable-speed electric drill that is slightly smaller than the diameter of the damaged screw or bolt that you need to remove.
Strike your metal tap with your hammer to make a small indentation in the top of the damaged screw or bolt. This small indentation is intended as a starting place for drilling a hole into the damaged screw or bolt so try to make your indentation as close to the center of the damaged head as you can.
Put a drop of machine oil on the damaged or broken head of the screw or bolt that you need to remove and then drill a shallow hole into the top of the damaged screw or bolt. Drill down far enough so that your drill extractor can fit down into the hole snugly. Wear eye protection when drilling.
Remove the drill bit from your drill and insert the screw extractor. Flip the switch on your drill (usually found near the start/stop switch) so your drill will run in reverse.
Insert the tip of the drill extractor into the hole you drilled into the top of your damaged screw or bolt. Slowly pull the trigger on your drill. As your drill turns counter clockwise the drill extractor will grab hold of the damaged screw or bolt and slowly unscrew it. Continue unscrewing the broken screw or bolt until it comes free. Always wear eye protection when running your drill.
When starting the extraction pull the trigger on your drill slowly so that the variable speed on your drill is working. You do not want the drill to start out at full speed when extracting a broken screw or bolt.