Tweco HD 24 Series Air Cooled Nozzles for Classic No. 4, Spray Master 450 and Supra 450 XT MIG guns are self insulated and compatible with HD54 Series Gas Diffusers. Used in heavy duty welding application up to 450 A. 3-piece nozzle design includes: Nozzle Housing - Cut and Formed from 122 DHP copper alloy tubing, Nozzle Insert - machined from a solid brass allows and is crimped in place to allow the nozzle to slide over a metal spring which is part of the gas diffuser, Nozzle insulator - made from G7 silicone material, providing the electrical insulation needed from the gas diffuser. Easy identification - Part No. rolled stamped on the outside surface. 3-piece design - does not require an additional insulator.