a method of manufacturing a columnar shaped piece formed of a thermoplastic matrix with ancillary pieces of a non - creeping hard material embedded therein and cemented by the plastic matrix . the ancillary pieces are essentially overlapping slabs which are substantially parallel to one another and the axis of the columnar shaped piece . molten thermoplastic blended with solid slabs is extruded in the form of a billet into one end of an elongate mold and rotated around the inner surface of the mold . the extrusion continues until the inner surface is uniformly covered with constituents of the billet .