These low cost diamond sharpening sheets measure 170 mm x 75 mm x 1 mm (6.7" x 3" x 0.040") and are made in China. We offer these as a budget alternative for sharpening and lapping. These are sheets, not plates and are very thin, so they need to be fixed to a flat substrate such as float glass, mdf, tile or metal plates using double sided tape or other adhesive. The diamonds are fixed to a thin steel sheet with electroplating, so if water is used as a cutting fluid, the plates will rust unless they are thoroughly dried after use or a rust inhibitor such a honerite is added to the water.
When these are firmly fixed to a flat surface, they are flat enough to use for general sharpening or flattening water stones, but likely won't be quite as flat as higher priced diamond plates from manufactures like Trend, Shapton, DMT and Atoma. They are probably flat enough to flatten the back of plane irons/blades, especially if you use the ruler trick, but we don't recommend them for flattening the backs of chisels. They are also idea for touching up carbide edges on items like the blades on wheel type marking gauges - best done by touching up the flat side on the diamond sheet.
For flattening water stones, we recommend using a coarse grit like the 240 grit sheet. The 240 grit, 400 grit, and 800 grit particles appear to be similar in size to other abrasives with the same grade of grit, but we would say that the 1200 grit, 2000 grit and 3000 grit have smaller particles than expected. We think that the most useful grits are the 800 grit and coarser, and haven't tested the finer grits. For those that can afford it, we really recommend sharpening with water stones such as Shapton glass stones for grits that are higher than 1000.
We recommend using either oil or water as a cutting fluid when using these plates, but when flattening water stones or ceramic stones, use only water, not oil! If mdf is used for the backing substrate, we recommend applying a thin film of a finish such as lacquer or varnish for water resistance.