Here's something a bit different in the flattening space - I usually hold the flattening stone and run it over my whetstone. This one works the other way round - you run the whetstone over the outsize flattening stone. It's a coarse stone, useful for flattening anything under #1000 or to do the initial flattening when a whetstone has been over used and the dip is significant.

Brand: Naniwa ナニワ研磨工業
Product Type: Flattening Stone
Grit: #24
Size: 302 x 151 x 20mm
Weight: 1943g