This Spot Weld cutter set includes 1 each of the following; 1/4 inch, 5/16 inch and 3/8 inch. (3 bits total). They are made from high quality Cobalt tool steel. Cobalt is even stronger the HSS. These are made in the USA. They work in common, inexpensive, electric or pneumatic drills. These are very popular spot weld cutters sold to production body shops. There pilot point is designed to cut easily with minimum penitration to the underlying panels. Included are instructions for spot weld cutting.