Suihei kun #100 Flattening Stone Sushi The composite construction of these AAEAA 020 4000 The composite construction of these boards makes for resistance to warping but avoid keeping one side of the board wet permanently to avoid fungus and warping This mix of chromium oxide has variety of abrasive particles formulated for the sole purpose of deburring steel The deep grooves made by the coarse 100 grit in the flattener will reduce the efficiency of the finer grit stones if they are not smoothed away This flattener is used in our shop for flattening stones under 500 grit as those extra coarse stones can damage diamond flatteners by wearing off the nickel plating holding the diamonds