Put plates back together again with the RED SURFACES UP, and insert the two10-32 screws and slightly tighten nuts. Screw the two 4-40 screws into the tapered holes and tighten to "seat" them. What we are doing is attempting to remove any machining irregularities that may have occurred that might allow shifting of the plates to occur at final assembly. Remove all screws and place to one side along with the bottom plate.