Securement of flat heat exchange surfaces, particularly fins to tubular conduits of a heat exchanger. The heat exchange material has longitudinal, partially circular recesses parallel to the length of a tube for engaging opposite sides of the tube. The radii of the recesses corresponds to the outer diameter of the tube. The recesses extend through less than 180.degree. so that the flat parts of the heat exchange surface are spaced prior to securement to the tubes. Forces are applied normally to the surfaces, forcing them together, stretching the heat exchange material at the recesses, thereby producing a tight interference fit between the heat exchange surfaces and the tube to provide minimum resistance to conduction of heat. Securement may be by spot welding, riveting, or otherwise. The tube remains round and undeformed so the cross sectional heat exchange area remains the same.