Abstract: A tube consisting of plastic or metal has a threaded tube neck which is sealed by a membrane and includes a cap with internal thread for mounting on the tube neck. The cap has projecting from its face a tubular punch member whose outer diameter correponds to the inner diameter of the tube neck and which has a circular cutting edge formed thereon for cutting the membrane from the tube neck when the cap is screwed or pressed onto the tubular neck. A retaining member is provided for holding the membrane in engagement with the punch member to prevent it from entering the tube.