Abstract: The invention provides a tool 10 of the invention for welding a PET gland 12 onto a PET bottle 14 for the fitment of a dispensing tap. The tool 10 is generically indicated as ultrasonic horn or sonotrode in the figure. The ultrasonic horn has a tapered serrated portion 16 which has a lead-in taper section 18 to initiate the melt of the plastics to be welded, and a knife section 20 (when required), being the cutting zone thereof, which in use cuts open a sealed spigot 22 so that the horn can enter into the spigot 24 for the welding operation.