The subject invention provides a heat exchanger assembly including a tank having a wall defining an aperture with a fitting secured thereto and a method of securing the fitting thereto. The fitting has a first end with an outer perimeter disposed exteriorly thereof and smaller than the aperture for inserting the first end of the fitting into the aperture. The fitting also has an internal tunnel extending along an axis thereto from the first end. A step of material is disposed in the tunnel at the first end, which is at least in part, radially and longitudinally displaced relative to the axis into contact with the wall to prevent rotational movement of the fitting in the aperture.