the invention relates to a plastic closure having a bottom part and a top part in order to make a tubular bag user - friendly and provide it with a secure closure . the bottom part has a flange on which a nozzle is integrally formed . the nozzle has a cylindrical part , in the region of which a form - fit means is attached to one side and an external thread located above is attached to the other side . a tapering , arched , conical part follows over the cylindrical part . the top part consists of a retaining ring , which is connected to a cap via a tightening strap . the retaining ring comprises form - fit means which engage with the form - fit means on the cylindrical part of the nozzle . the retaining ring is thus held on the nozzle in a rotatable but axially fixed manner . the cap has an internal thread which clamps with the external thread of the nozzle .