The WÜSTHOF 9" Fine Diamond Knife Sharpener with a diamond coating, should be used for dull or moderately sharp knives. The special shape of the diamond grit on the sharpening rod ensures exceptional sharpening of the knife blade. The result: a smooth, sharp edge. This sharpening rod has a fine grit. As these rods remove a tiny amount of metal from the knife, we recommend an additional WÜSTHOF Honing Steel for daily or weekly maintenance.