The fabrication of a heat exchanger assembly by disposing a metal fitting of an oil cooler subassembly into an opening in a first tank and disposing a tubular connector into a bore in the fitting. These components are mechanically held together prior to brazing by disposing an outer clinch cylinder to extend from the fitting though the opening and by disposing an inner clinch cylinder to extend from the fitting to above an annular rib on the tubular connector and placing V-shaped first stakes in the inner clinch cylinder for mechanical engagement with the rib and placing V-shaped second stakes in the outer clinch cylinder for mechanical engagement with the first tank.