Abstract: In a grinding mill, a polymeric filler material is molded into the rectangular or prismatic recesses in a metallic or ceramic lining. In a grinding mill where longitudinally extending elongate ribs of the lining have two different radial thicknesses or heights, with relatively narrow bars and relatively thick bars alternating with one another, the filler material is initially cast to have a cylindrical or undulating inner surface. Where the surface is cylindrical, the filler material is worn away during use of the grinding mill and gradually conforms to the alternating narrow and thick bars to assume an undulating inner surface. Supplemental lifter bars may be embedded in the grid and rubber filler material during the casting process. Where the lining is assembled from elongate wedge-shaped metallic or ceramic bas and spacers, the bars and spacers are provided in modular forms with the spacers as wing-like extensions on the bars. Ceramic or other hard particles are embedded in the filler material.