An apparatus for connecting first and second seat areas is provided. The first and second seat area extend substantially with each other and each of the first seat areas have a corresponding second seat which it is connected to. The apparatus comprises a receiving bore fixed to one of the first and second seat areas. A threaded stem penetrates at least one connected set of the first and second areas crosswise through the receiving bore. The threaded stem has a conical spreading area and bears a nut on the side opposite the conical spreading area such that the threaded stem is freely movable axially on one side. A spreading bush encompasses the threaded stem. When the threaded stem is tightened by means of the nut, the spreading bush spreads outward over the conical spreading area and a face of the spreading bush rests firmly against one of the seat areas, an inner contour of the spreading bush rests firmly against the conical spreading area, and an outer periphery of the spreading bush rests firmly against an inner wall of the receiving bore.