Estone Ruby Sharpening Polishing Whetstone Oilstone Grit 3000 Sharpening Tool Sharpener The Ruby Sharpening stone is made from sintered crystals of synthetic ruby It's extremely hard, maintain their shape well and are resistant to wear Install easy in the a tool or machine, also 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