A TIG cup number tells you the nominal opening size, not which torch it fits. A #6 cup typically has a 3/8-inch outlet, but the #6 cup on a 9/20-style torch is not necessarily interchangeable with a #6 on a 17/18/26-style torch. You must also match the cup family to the torch head and to a standard collet body or gas-lens arrangement. Here is how to choose without ordering the right number and the wrong part.
What do TIG cup numbers mean?
In common numbered TIG nozzle families, each whole cup number corresponds to one sixteenth of an inch of nominal outlet opening diameter. For example, a #4 is 4/16 inch (1/4 inch), a #6 is 6/16 inch (3/8 inch), and a #8 is 8/16 inch (1/2 inch). This is the opening, not the outside diameter, thread size, tungsten size, gas-flow setting, or torch model. Manufacturer dimensions and fitment still control, especially for glass, large-diameter, stubby, specialty, or nonstandard cups.
| Common cup number | Nominal opening | Selection question |
|---|---|---|
| #4 | 1/4 in. | Does the smaller opening give enough coverage in the actual joint and torch position? |
| #5 | 5/16 in. | Is it the desired midpoint, with correct hardware family? |
| #6 | 3/8 in. | Will it clear the joint while covering the tungsten and hot puddle? |
| #7 | 7/16 in. | Is more coverage needed without obstructing the view? |
| #8 | 1/2 in. | Is the larger outlet appropriate for torch access and shielding needs? |
| #10 | 5/8 in. | Does the setup support this larger cup and an appropriate shielding arrangement? |
CK Worldwide identifies these numerical cup and part-number relationships in its 2 Series torch parts chart and 3 Series torch parts chart. Use the specific part number on your existing nozzle or torch assembly to determine the proper replacement family.
Choose the torch family before the cup diameter
2 Series: common 9 and 20 style torch parts
CK lists a 2 Series (13N) family for torch models 9 and 20. In that standard alumina family, #4 is 13N08, #6 is 13N10, and #8 is 13N12. These are not the 10N parts used on many larger torches. If your installed head uses the standard 2 Series arrangement, consider the stocked 13N08 #4 alumina cup 10-pack for smaller access openings or the 13N10 #6 alumina cup 10-pack for a larger opening. Both require the correct matching collet body and associated components; a shared cup number does not prove fit.
For a still larger outlet within that same standard family, Arc Weld also lists the 13N13 #10 alumina cup 10-pack. Do not substitute a #10 simply because it is available: access around the joint, gas behavior, and the torch manual matter more than the largest number on the shelf. CK's 2 Series list provides the underlying part family.
3 Series: common 17, 18 and 26 style torch parts
CK's 3 Series (10N) family is associated with 17, 18, and 26 torch models. Its standard alumina part numbers differ: #4 is 10N50, #6 is 10N48, and #8 is 10N46. Arc Weld has the 10N50 #4 cup 10-pack, the 10N48 #6 cup 10-pack, and the 10N46 #8 cup 10-pack in this standard family. Choose between them based on the job, not on a claim that a #8 makes every TIG weld cleaner.
For exact hardware matching, consult the CK 3 Series component chart. It lists standard collet bodies, gas lenses, heat shields, and cups separately. If a shop has both 9/20-style and 17/18/26-style torches, label spare cup bins by series, part number, and cup size to prevent mixing look-alike consumables.
Standard cup versus gas-lens cup: why the part number changes
A gas lens is a different collet-body arrangement intended to manage shielding gas distribution. It uses the compatible gas-lens cup and required insulator or heat shield, rather than assuming a standard nozzle will fit. CK's 2 Series chart identifies a #6 standard alumina cup as 13N10 but a #6 gas-lens alumina cup as 53N60. Arc Weld stocks the 53N60 #6 small gas-lens alumina cup 10-pack for the listed setup. Its size is not proof that it fits a standard 13N collet body.
For CK 3 Series parts, the manufacturer chart similarly lists a #6 standard cup as 10N48 and a #6 gas-lens alumina cup as 54N16. The 54N16 / CK 3AG6 #6 gas-lens cup belongs to that separate family. When converting a torch to a gas lens, verify the whole stack—torch head, collet and gas-lens body, insulator, tungsten diameter and cup—against the correct parts chart. Our TIG collet and collet-body fitment guide explains how the gripping components fit into that decision.
A glass cup, stubby conversion, or large-diameter gas lens may use an entirely different mounting arrangement. No single opening size or color proves compatibility; do not force a cup onto mismatched threads.
How to choose between a #4, #6 and #8 for the actual weld
Start with joint access and shielding coverage. A smaller cup can make it easier to reach a tight corner, but the gas envelope still needs to protect the arc and hot metal. A larger cup can provide a wider outlet but may block a narrow joint or interfere with torch angle. In either case, the practical variables include the torch type, cup shape, tungsten extension, gas lens, base metal, joint geometry and surrounding airflow. Those conditions matter more than a universal “best cup size.”
Do not turn nominal cup diameter into a fixed flow-rate prescription. Appropriate argon flow and tungsten extension depend on the machine and torch specifications, gas equipment and application. More flow is not automatically better: excessive flow or drafts can disturb effective shielding. Use the manufacturer's recommendations and a qualified welding procedure specification (WPS) where applicable. If weld appearance is poor, first investigate contamination, gas leaks, incorrect polarity or preparation, shielding interruptions, and consumable damage rather than buying larger cups blindly.
Quick replacement checklist before ordering
- Identify the torch model and series. Read its nameplate, manual or installed torch-part diagram; do not assume every TIG torch on a shared machine uses identical front-end parts.
- Identify the installed collet-body style. Standard, gas lens, large-diameter gas lens and stubby systems have different cup families.
- Read the exact cup or part number. A #6 from one family does not replace a #6 from another family.
- Confirm outlet diameter and access. Compare the required weld area and torch angle, without assuming larger is always safer or more effective.
- Inspect the mating components. Replace cracked cups or damaged insulating hardware using the applicable equipment manual; do not conceal heat or electrical damage by simply changing the nozzle.
- Confirm pack quantity. The Arc Weld examples in this guide are sold under their listed package quantities; check the actual selected listing before ordering.
Before inspection or component changes, switch off the power source, isolate energy as instructed and allow the torch and consumables to cool. Use appropriate eye, face, hand and ventilation protection for the welding operation. OSHA's 29 CFR 1910.252 welding-safety requirements provides applicable workplace safety context; it is not a replacement for the specific equipment manual.
Frequently asked questions
Does a #6 TIG cup fit every TIG torch?
No. The nominal outlet is the same general size, but a #6 cup can belong to different 2 Series, 3 Series, gas-lens, or specialty fitment families. Match the full part number and torch assembly.
Is a #8 cup always better for aluminum or stainless steel?
No. Both processes need appropriate shielding, but cup size alone does not establish the right gas flow, stickout, or access for an application. Check the torch manual and WPS.
Can a standard cup be reused after switching to a gas lens?
Not by default. CK lists separate standard and gas-lens cup part numbers. Verify the actual conversion-kit parts list and required heat shield before reusing anything.
Bottom line: choose the torch and collet-body family first, then cup size. The number tells you the opening; the manufacturer part number tells you which hardware it belongs with.