Abstract: A discoid element (7, 8) for a helical screw or worm arrangement comprising, on each side, identical shallow depressions (20); each depression having an open end (21) adjacent the periphery and a closed end (22) adjacent a central bore (23). The depressions (20) in one side of the discoid element are staggered with respect to those of the other side. The discoid element may also contain radial ribs (24, 25, 26, 27) constituting the sidewalls of the shallow depressions. The discoid elements may suitably be used in apparatus for dehusking grain.