Ultra fine stone tightens the blade scratch pattern to an even keener degree for hair-popping professional sharpness and polishing. Fits the 204 Sharpmaker system, stones are sold individually. 204UF TriAngle stones are 7" X 0.5" (178 mm x 1 3mm). For cleaning: scrub with a scouring pad and powered abrasive cleaner, air-dry. Autoclave safe.