Stopper

The present invention relates to a closure plug (10) for closing an opening (O), in particular in a vehicle body, having an annular sealing section (12) which is provided to bear against the edge of the opening (O), and an expansion section (14) which is formed integrally with the sealing section (12) and is adjustable from an assembly position, in which the sealing section (12) has an assembly diameter at least at one axial end, into an expansion position in which the sealing section (12) has a larger diameter, wherein by adjustment into the expansion position the sealing section sealingly bears against the opening edge or the opening inner surface.