This set of 7 Irwin(r) Power Grip Screw Extractors have reverse spiral flutes for maximum gripping power. The universal shape fits metric and fraction sizes. Featuring a 1/4in hexagon shank suitable for use with power drills and nut drivers, they will easily extract rounded off rusted tight and painted over bolts. They are made from durable high carbon steel for a longer life. Supplied in a durable plastic case. Specifications: Sizes: 8mm, 10mm, 11mm, 3/16in, 1/4in, 5/16in, 3/8in, 7/16in, 1/2in. Drive Size: 1/4in.