I bought these on a whim basically just to see if they were any good. They cost 12 bucks for the 3 diamond plates, color coded all 6"x2" made by Cal-Hawk. Yellow is 150 grit, red 250, and blue 400 grit. I block mounted them onto some lapped wooden blocks to keep them flat while lapping. I have to say I guess I got lucky because the grit ratings are accurate. I have lapped quite a few stones with them, and used the blue 400 grit for quick bevel setting on several razors so far and the diamonds are still attached and sharp (I expected them to rub off). I haven't had any problems with the corrugated surface, but these ones are small and oval. The blue 400 gets the most use so far, the other 2 are basically for serious lapping but over all I'm pleasantly surprised with them.