Super-hard, pure polycrystalline cuts tool steel, hardened steel and tungsten carbide. Perfect for final honing. These stones cannot be classified in terms of "grit" but only in terms of the average grain size. The average grain size of types "fine" and "medium" is about 10Amicro (microns). Mfg: Gesswein SPECS: No. 221 Flat – 4" (10.2cm) x 5/16" (8mm) x 1/4" (6.3mm). No. 291 Knife – 4" (10.2cm) x 5/8" (15.9mm) x 1/8" (3.2mm).
