Atoma Tsuboman spare replacement diamond sharpening plate extra fine #1200.

This is only the 1 mm replacement plate, without the 1 cm thick aluminum plate. It can be also glued on a piece of glass or any perfectly flat surface. 

Atoma "Economy" line stones have their monocrystalline diamonds fixed to a 1 mm thick stainless steel plate that is then fixed with double sided tape to a 10 mm thick aluminum plate (Not included).
You can sharpen knives, chisels... and it can be also used to flatten your waterstones.

Size : 210 mm x 75 mm x 1 mm
(8.3" x 2.9" x 0.04")
Weight : about 120 grams

Unlike whetstones that can become rounded or hollow, which decrease their effectiveness, diamond plates remain flat. 
They do not require the use of a lubricant, but you should wet the surface with water. Also avoid too much pressure during the sharpening process. 

Made in Japan.