Abstract: In order to grade or classify particles according to their sphericity, the particles are fed onto a moving surface which has a gentle slope in the direction transverse to the direction of movement so that the particles move down the slope while being carried along by the moving surface. The rate of movement down the slope depends on the particle shape so that particles of different shape reach the lower edge of the surface at different positions. This movement of the particles is facilitated by vibrating the surface or moving it intermittently. The surface is preferably a rotating disk.