How can I remove a stripped screw that won’t turn?

A screw extractor (or screw remover set) is specifically designed for this problem. First, drill a small pilot hole into the center of the stripped screw head using a drill bit slightly smaller than the extractor. Then, insert the screw extractor bit into the hole (it has reverse threads). Using a drill (in reverse) or a tap wrench, turn the extractor counter-clockwise. The extractor's threads bite into the screw, allowing you to back it out.

Place a wide rubber band flat over the stripped screw head. Press the tip of the correct size screwdriver firmly into the screw head through the rubber band. The rubber band fills the gaps in the stripped head, providing extra friction and grip. Turn the screwdriver slowly and firmly counter-clockwise.

If enough of the screw head is exposed above the surface, clamp locking pliers tightly onto the outside edges of the screw head. Once gripped securely, slowly twist the pliers counter-clockwise to loosen and remove the screw.