Flexi Drills Slim Line High Speed nail chewing drill bits are mounted on a 3/16 inch ultra flexible shaft with fishing wire accommodation on the flute as well as the shaft. Highly recommended for areas construction materials consist of nails, steel plates, sheet metal and other items of a similar nature as well as wood structures. Slow back taper allows the bit to retrieve easily. To sharpen bit use a bench grinder or a drill sharpening mechanism.