Back caps come in 3 sizes:
The back cap applies pressure on the collet. This holds the Tungsten electrode in place.
A new Tungsten electrode is normally about 7″ (175mm) long. As the Tungsten electrode gets shorter, you can change the back cap to a smaller size. A smaller back cap allows the TIG torch to be used where space is restricted. So keep some shorter Tungsten electrodes back for this purpose, rather than using them up completely.
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