For deburring and sharpening edges.
If you like your board or skis to be catch free, de-tune 2" north and south of the contact zones, 4 points of contact. Use a Gummy or a Ceramic Stone. Start on the edges as they curve up into the tail and nose and dull lightly approximately 2" from being flat on a table in both directions for a total of 4".
Sold in singles.