<p>In a slide fastener having continuous coupling elements of the helicoidal-coil type, a bottom stop is formed by imparting ultrasonic vibrations to the several interengaged lowermost scoops of the coupling elements, while these scoops are being compressed from opposite lateral sides thereof to move the coupling heads of each element into abutment against a core received in the other element. The ultrasonic vibrations are applied by the horn of an ultrasonic welding assembly holding the interengaged lowermost scoops from both front and rear sides of the fastener. The invention is also applicable to a slide fastener having zigzag-type continuous coupling elements.</p>