Estone 400 800 Grit Double Sided Boron Carbide Knife Sharpener Stone Whetstone Tool Boron Carbide stone is extremely hard, maintain their shape well and are resistant to wear. Easy sharpening and polishing all kinds of exact knives. For sharpening and polishing chilled steel, alloy steel and precision parts etc. Sharpening stone can use oil or water. Material: Boron Carbide, Model:400 & 800 Grit