<p>The grinding body has a shape similar to a triangular prism, made of three arcs, (5). The prism is confined by the base and top faces (2). In one version the edges of the base and top of the prism are rounded. In another version the base and top of the prismatic triangular body are shaped as spheroidal triangular pyramids, whose base is the cross section of the prism. I another version at least one vertex of the pyramids made on both sides of the prismatic body is cut flat. In another version the edge of either the base or the top face of the grinding body is surrounded by a ring (11). In another version the base or both base and top faces of the prism are made as convex parts of a sphere or of another three-dimensional figure.</p>
