Abstract: A coupling including a first hollow section having longitudinal corrugations and a second section having an aperture therein. The coupling is made according to the method including the steps of inserting the first hollow section having longitudinal corrugations into the aperture in the second section so that at least a portion thereof including the corrugations extends into and beyond the aperture, the first hollow section being selected so that its cross-sectional length exceeds the perimeter of the aperture. At least the portion of said first hollow section beyond said aperture is then expanded so as to smooth the corrugations, while avoiding stretching the wall of the first hollow section whereby the exterior size of the hollow section exceeds the entire perimeter of the aperture and the cross-sectional length remains unchanged.

Abstract: A hollow section for coupling to other sections and methods for the production and utilization thereof. Hollow sections are formed from strip or sheet material which are corrugated and then welded along a longitudinal seam. The thusly formed corrugated hollow sections are inserted into another section and flanged on or coupled thereto by smoothing or expanding the corrugations. The length of the corrugations is selected to be substantially equal to the circumference of the aperture into which the hollow section is coupled.