If you have a stuck screw or bolt and have mangled the head, try removing it with a special screw extractor. It usually does the job quickly and easily.
Drill a hole in the center of the broken screw or bolt using the drill bit size specified by the extractor manufacturer.
Tap the extractor into the hole and turn it counterclockwise with locking pliers or a tap wrench to remove the screw.
Extractors are available in several sizes to fit the approximate screw size.
When you twist the head off a bolt, break a screw shank or mangle a screw head, you have a few options: In metal, you can completely drill out a bolt and restore the damaged threads with a tap. Likewise, you can drill out a wood screw and replace it with a larger one. But before you try these tricky methods, try a screw extractor, which usually does the job quickly and cleanly. You'll find extractors at home centers and hardware stores for screw diameters from 3/32 in. to 1/2 in. or larger. Small extractors cost about $4.
Start by drilling a hole in the center of the screw (Photo 1). If your drill bit won't stay centered on the jagged, broken surface, switch to a smaller bit (1/16 in. or smaller). A smaller bit is easier to control and creates a shallow starter hole for the larger bit. Drill cautiously and apply only light pressure. The worst thing you can do is break off the drill bit inside the broken screw because removing a broken bit is almost impossible.
Next, insert the extractor and give it a firm tap with a hammer. Then push down on the extractor as you twist it counterclockwise (Photo 2). If the extractor threads won't grab and turn the screw, try these other suggestions: