Abstract: An annular metal fitting permanently attached to an outer, cylindrical surface of a rigid plastic part. The metal fitting is tapered inwardly from an inside diameter larger than the outside diameter of the plastic part, to an inside diameter smaller than the part, forming a first annular tooth within the fitting. A second annular tooth is similarly formed, but with an inside diameter less than that of the first-mentioned tooth. Axial grooves in the fitting prevent relative rotation of the fitting and plastic part after joining of the two by ultrasonic welding.