I was eyeballing these Naniwa Chosera round stones for a while.
With a few 270mm knives, a 400mm Nakiri in the collection and the aspiration to get me a 300mm+ (hopefully 450mm) Sakimaru one day, they seemed so handy.
They come in 320/1000/3000. I bought myself a 1000 and 3000. The 320 was unfortunately sold out. The normal Chosera stones don't even come in 320. It only exists in this round version.
I also got two stone holders for them in which they fit perfectly and are made of a hard type of rubber, so it won't slide on any smooth surface.
These are in fact stones for free hand sharpening longer blades. Not for a rotation machine of any kind. Although I can imagine it would be cool to mount it on a pottery wheel or record player for some spinning action.
They are not only huge and round, they are also 27mm thick! Which is a lot of Chosera stone right there.
These stones are available at:
USA - perfectedgecutlery.com/
(they're not listed on the website, but e-mail them: Tara Ransfer and her team will give you the service you need)
Europe - www.knivesandtools.com/en/pt/...