This extra large flattening stone by Naniwa will tackle any water stone flattening needs. This is the largest flattening stone we carry (by a long shot).
If you feel that your flattening stone should be gigantic, this is your stone. This measures 300MM x 150MM x 20MM. If you do your measuring in inches, that makes this stone almost 12" long, 6" wide and an inch thick. With this sort of heft, this is not the type of flattening stone you can hold in your hand. Solid rubber feet keep this stone planted firmly so you can focus your efforts on the water stone in your hand. This stone is 220 grit.
Made in Japan.
Q. Do I need a flattening stone this big for my water stones?
A. No way. This stone is really really big. However, some people prefer to have their flattening stone secured to the surface so they can put their water stone in their hand and flatten it on the stone. If you have larger water stones and your budget allows, this a nice flattening stone.