A screw whose head has been worn and ruined by previous screwing is difficult to unscrew again. The screwdriver can no longer grip properly and slips off. Even without special tools, you can unscrew a broken screw using a rubber band. Place a wide rubber band, wide enough to cover the screw head, between the head and the screwdriver. The screwdriver should be slightly larger than the one that wore out the screw. Press the screwdriver firmly onto the rubber band and slowly and forcefully try to turn the screw. The rubber band gives the screwdriver enough grip to loosen the screw, as the rubber band lies in the gaps and provides grip. Once the screw is slightly loose, you can use pliers to unscrew it completely.