The Coarse diamond wheel is a replacement grinding wheel, with a coarser grit. It is ideal if you have damaged knives and want to be able to remove a lot of material quickly to repair the edge. It also has a diamond coating on the flat side of the grinding wheel, which is particularly helpful when you have to repair a damaged knife by removing a lot of material. 
350 Grit, Sharpens all steel qualities including ceramic knives, Removes more material than fine and extra fine wheels, Easy to Mount.