The unit is joined to the vehicle with a carrying element (1) accommodating the shaft of a pivotal ball holding element (3) provided with a calotte fixing device (6) vertically moved by a pivot (7) also serving as a vertical axle. The rotation axis of the unit leads through the center of the carrying element (1) as well as through the center of the ball element (4) resulting in a stable pulling action independent of the position of the towing unit.
