This flattening stone from Naniwa is designed to keep your Naniwa Waterstones in optimal condition.
Stone measures 170mm x 55mmx 30mm. It has a 220 grit.
Made in Japan.
Mark the upper most side of your waterstone with pencil with a cross hatch design. Wet the flattening stone before use and wet your waterstone as required. Place the waterstone on a stable work surface and then rub the flattening stone over it until the waterstone is flat and there are no pencil marks left. You will need to rinse the flattening stone several times during use to remove deposits.