Forney 60139 Tungsten Carbide Burr with 1/8-Inch Shank, Cylindrical, 1/4-Inch Shank mounted tungsten carbide burrs are double cut for fine work Designed for use on ferrous metals, plastic, fiberglass and other machinable materials Great for deburring, sculpting and removing material in hard to reach areas Designed for use with high speed die grinders Max RPM is 90,000