A TIG gun (torch) can have various interchangeable parts fitted. These interchangeable parts (along with the TIG welder controls), enable you to weld a variety of materials, and their different thicknesses.
Some parts are literally consumables, they get eaten up during the welding process. Other parts are consumables, due to wear and heat degradation. These parts may last longer (and only get replaced when worn, or when changing the torch configuration).
Torch parts must match the TIG torch (or the group of torches) being used, (see the article TIG Torch – The Different Types:). Some parts are also dependant on the size of the Tungsten electrode fitted. I.e. if you are using a 1.6mm (1/16″) Tungsten electrode, then the collet and gas nozzle must also be 1.6mm (1/16″).
The image below shows a typical collection of TIG torch parts and how they fit together:
More detail on each of the TIG torch consumables can be found by following the links below: