The winding gears usually have a left hand thread. This will be a relitavely small screw with a large head. Always make sure of the direction required before attempting to unscrew these large headed screws. These screws usually unscrew in a clockwise direction. Before attempthing to remove the stud you still must have this information. If you have access to a drill press or a lathe get a small milling cutter and mill a flat on the top of the broken stud. Then select either a left or right hand drill bit that will drill in the direction that unscrews the broken part. You may have to make your own drill bit to do this. Put a few drops of liquid wrench or diesel fuel on the stud to allow it to soak in around the threads. Drill it out in the direction that unscrews it and keep your fingers crossed.