A coupling of a heat exchanger includes a saddle for engaging a cylindrical manifold. The saddle has an arcuate cross-section extending between a first edge and a second edge. The saddle defines an opening and a tubular member extends through the saddle and between a top edge and a bottom edge. A lip extends outward from the top edge and a skirt interconnects the lip to the opening in the saddle. The tubular member is oblong-shaped adjacent the opening of the saddle and the tubular member has an oblong-shaped portion extending from the bottom edge to adjacent the opening in the saddle and terminating at a transition zone. The tubular member has a circular-shaped portion extending from the transition zone to the top edge. The oblong-shaped portion has a shorter dimension in the direction between the first and second edges than the circular shaped portion.