Description: Removes broken screws, bolts, and studs without damaging bolt or hole threads These stud / screw extractors will remove any stud / screw pipes and bolts. Covers bolts from 3mm to 18mm. Can be used with a spanner / socket or even holder on the end of each spiral extractor. Designed to remove studs, bolts, screws, stubborn, rusted, stripped, screws or bolts, even factory installed carriage type bolts with no slots to remove from. Screw Extractors Type: 3-6mm/ 1/8-1/4 inches 6-8mm/ 1/4-5/16 inches 8-11mm/ 5/16-7/16 inches 11-14mm/ 7/16-9/16 inches 14-18mm/9/16-3/4 inches.