Made of hardened steel, the screwdriver bits in this set are magnetized to remain securely in place in your drill/driver, and have been heat-treated for a longer life. Their optimized design helps prevent them from slipping out of screw heads. Each bit has a shank diameter of 1/4-inch. The set helps you drive screws straight and quickly, and a pair of magnetic nut drivers to tighten nuts and bolts.