Designed to remove broken studs, bolts, socket screws and fittings. Aggressive left hand spiral design for extra gripping power. Spiral flutes are designed to embed themselves deeper into the metal as you turn the tool, so as the fastener resistance increases, the extractor's grip increases. Extractor size and recommended drill bit size are etched on each tool. Set include bolt extractors to remove bolts sizes 8, 11, 14, 16, 19 and 1/4, 5/16, 3/8, 7/16, 1/2, 9/16, 5/8, 11/16, 3/4 in drive size 3/8 inch.