The 400/1000 Combined Sharpening Stone is an essential tool for keeping your knives and other cutting instruments in perfect condition. Made of corundum, this water sharpening stone has two different sides for complete sharpness. The coarse-grained GR 400 side is ideal for repairing notches, grinding blades or sharpening very blunt knives, removing a large amount of material. On the other hand, the finer grained GR 1000 stone allows finer adjustments or finishes to be made to the blade. This stone is perfect for both professional and amateur chefs.