Norton Crystolon Fluted Hand Rubbing Brick with Handle, 6" Length x 3" Width x 1" Height Hand rubbing brick (also called abrasive block) for rubbing concrete and removing mold marks Fluted surface has diagonal grooves with sharp edges for debris removal and clean shearing action Silicon carbide (Crystolon) is more aggressive and cuts faster than aluminum oxide C20 extra-coarse grit size for faster cutting than abrasives with a finer grit Firmly bonded handle facilitates overhead, floor, and wall jobs