Abstract: An opening stopper of elastomeric material, especially for sealing lacquer outflow openings in automotive vehicle bodies, comprising a closed bottom, an elastically shapable flange covering the edge of the workpiece opening, a collar connecting the bottom to the flange, and a shoulder disposed at the outer surface of the collar, said shoulder engaging behind the oppositely disposed opening edge, wherein the shoulder is formed by a circumferentially extending free edge of a lip configurated like a conical disc which is tied at a location level with the countersunk bottom and extends obliquely outward towards the flange.