Stark 9-Pieces spiral screw extractor sets feature extractors that are ideal for removing stripped screws, bolts and other fasteners. The left-hand flutes grip the metal firmly. Spiral flutes are used to remove stripped screws from harder materials (straight flutes are for removing stripped screws from softer material). The screw extractor are made from heat-treated carbon steel, they are rust and tarnish-resistant tools. Designed to remove broken studs, bolts, socket screws, fittings, stripped screws and other fasteners. 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. Aggressive left hand spiral design for extra gripping power. Extractor size and recommended drill bit size are etched on each tool, Heat-treated carbon steel provides superior durability. Size: large.