The Mt. Sun Gear Gummi stone is a must have for your tuning kit. It allows you to get your edges truly sharp by removing microscopic burrs caused by filing your edges. Once you are done with files and diamond stones, rub the Gummi along the edge of the length of your ski or board for a super smooth smooth finish. Then, use it to detune the tips and tails of your board or skis to reduce the chances of catching the edge. Or keep it in your pocket to remove those pesky burrs caused by really hard snow- it will make the edge grip and hold again till you can get it back to your tuning bench for a proper tune. It will also remove pesky rust if you forget to dry your ski or board after Apres!