the end joined to the connecting member the openings in the edge region of the profile and those in the edge region of the connecting member are superimposed for joining cup impressions are formed in the region of the openings in the profile the cup impressions allow a positive connection without any play between the connecting member and the profile alternatively or in addition to the openings with or without impressions in the edge region of the connecting member and the edge region of the profile beads may also be provided similarly allowing the profiles to be positively connected to the connecting member additionally or alternatively an adhesion or welded joint may for example provide a material connection between the connecting member and the profile in addition to the positive and if appropriate material connection between the connecting member and the profile thermoplastic may be injected through and around the openings to achieve the desired tenacity the same plastics material may be used for the injection of thermoplastic as for the reinforcing ribs the ring joined to the free end of the profiles is preferably made of the same plastics material as the reinforcing ribs it may however independently of the ring sic be made of a non reinforced reinforced and.