Pyrex cups can come as standard or narrow TIG nozzles. Standard Pyrex cups are 19mm in diameter. The larger area is used to provide for a more spread-out area when welding reactive metals like titanium, molybdenum and nickel or aluminium based alloys as well as non-reactive metals like stainless steel. Tapered nozzles have a narrower tip, and at 13mm is the ideal TIG nozzle in tighter welds and when consuming less argon shielding gas is a priority. 
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