Heretofore, others have fastened axially extending bars or channels to the inside of the cylinder cage or concave to retard the axial flow of crop material so as to subject the crop material to increased threshing as it passes through the threshing section of the harvester. 
U.S. Pat.  No.  3,529,645 illustrates a spiked threshing rotor cooperating with cob grinding and corn kernel cracking spikes on the casing surrounding the rotor.  U.S. Pat.  No.  3,618,616 shows spikes secured to the threshing rotor, the concave and the interior wall of the cylindrical casing to comb or rake the straw when operating in weedy or damp straw conditions or when harvesting rice.