Japanese Flattening Stone (For Whetstones)A simple, dependable tool to keep your sharpening stones true. Use it regularly to level the surface of your water stones and restore that perfectly flat plane essential for an even, consistent edge. Over time, whetstones naturally wear into a shallow hollow through use. A few light passes with this flattening stone kept wet and used often will bring them back into alignment. No abrasive powders required, just water and attention.