These hollow ended screw extractors will quickly & easily remove screws without damaging the surrounding area. To extract broken screws rotate the hollow extractor bit counter-clockwise slowly down over the screw, the bit should engage & unscrew it or the core around it. To avoid "dancing" guide it with a thru hole in a scrap piece of wood clamped in place  (with the same hole size as the extractor in use). Size refers to the finished hole size.,
Screw Extractor for Wood