Bob Kramer is widely recognized for his extremely sharp high performing carbon steel knives. To keep these knives maintained and sharp, Bob Kramer by Zwilling has introduced an entire collection of water stones. Each water stone is made from a synthetic ceramic. Depending on your preference or needs, this collection offers 5 grains to choose from. Grit #400- is used for changing the angle of the edge, edge repair and will create a long lasting sharpness. These stones are safe to use on all knives except ceramic.