Narutaki Hachiman Toishi Sharpening Stone.
200mm x 73mm x 32mm in thickness.
This stone is an Asagi-type professional-size and quality sharpening stone. When it is wet with water (as in a couple of the photographs) the stone looks dark and black. When dry, it is gray.
 
This is a razor-grade stone that, with the tomonagura will hone a wide range of steels. The tomonagura is included.
 
The knife in a picture is mine for testing and not for sale.