Annular metal fitting for rigid plastic part

The combination comprising:

• a. a rigid plastic part having an end portion with a cylindrical external surface of a first diameter;
• b. an annular metal fitting having first and second ends and an internal bore extending therethrough to define an internal surface;
• c. said fitting being of a second diameter at said first end and a third diameter at said second end;
• d. said internal surface sloping inwardly from said first end, around the entire periphery thereof, at a predetermined angle of between 8.degree. and 18.degree. to a fourth diameter, said first diameter being smaller than said second diameter and larger than said third and fourth diameters, said fourth diameter being larger than said third diameter;
• e. said internal surface extending radially outward from said fourth diameter to a diameter equal to said second diameter, thence sloping inwardly at substantially said predetermined angle to said third diameter, thence extending radially outward to said second diameter, thence sloping inwardly at substantially said predetermined angle to said third diameter, thence extending axially at said third diameter to said second end, thereby forming a plurality of teeth and grooves;
• and
• f. ultrasonic welding means for permanently joining said plastic part and metal fitting with said external surface opposing said internal surface over the entire area of the latter, whereby high frequency vibrations causes friction between the metal fitting and the plastic part which generates sufficient heat to soften the plastic part to flow around the teeth and into the grooves.