Astro 2181 Double Cut Carbide Rotary Burr Set with 1/4-Inch Shank 8-piece Double Cut Carbide Rotary Burr Set Perfect for opening holes, or porting heads on ferrous materials Sintered and machined from 100% new raw tungsten carbide Unique tooth angle prevents chipping for the longest lasting design possible 1 year warranty from manufacturer with simple replacement process