4 Color coded synthetic sharpening stones in different grits made of aluminum oxide.

Evaluators reported the following advantages:
      a)  Very Easy to Use
      b)  Restores edge quickly & well
      c)  No oil needed during sharpening
      d)  No metal build-up on stone during sharpening
      e)  Sterilizable

RED - Coarse
BROWN - Medium
BLUE - Fine
BROWN & BLUE is combination stone {medium & fine}