DMT A4E 4-Inch Diamond Whetstone For Use With Aligner - Extra-Fine Superior diamond sharpening stones Legendary quality Made in the USA Portable pocket convenience Extra-Fine diamond to polish and refine an edge Sharpens knives faster than conventional stones with DMT's monocrystalline diamond surface No oil is needed-sharpen dry or with water Durable construction will provide years of consistent performance and reliable service