What's inside
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The cup on a TIG torch is more than a nozzle: its opening affects how widely shielding gas spreads, how easily the torch fits around a joint, and how much the weld is exposed to drafts. A larger cup can improve coverage, but it will not compensate for poor gas flow or a bad torch angle. Choose the smallest cup that gives the joint reliable shielding and leaves enough room to work.
What cup size means
Most TIG cups use a numbered sizing system. In the common numbering convention, the number is the cup’s inside diameter in sixteenths of an inch. A No. 6 cup is about 3/8 inch (9.5 mm) across; a No. 8 is 1/2 inch (12.7 mm). Verify the dimensions for your torch and cup type, since products and systems can vary.
Numbers describe the opening, not the shielding performance by themselves. Gas lens cups often provide smoother gas flow than standard collet-body cups, which can help when using a longer stickout or working in a confined position. They still need compatible torch parts. Check the torch model and consumable system before ordering.
Start with joint access
Look at the approach angle and the space around the weld. A cup that hits a flange, tube, or neighboring part can force you to tilt the torch too far or hold it farther away. Either change can weaken shielding and make it harder to keep the tungsten, arc, and filler wire where they need to be.
For open, flat work, a No. 7 or No. 8 cup is a useful starting point. For tight corners or narrow gaps, a No. 4 to No. 6 may fit better. If a small cup lets you reach the joint only by dragging it against the work or sharply angling the torch, try a smaller torch head or a different joint setup rather than forcing the fit.
Match cup size to the task
| Typical use | Starting cup range | Main trade-off |
|---|---|---|
| Thin sheet, tight corners, small parts | No. 4–6 | Better access; less margin against drafts and torch movement |
| General bench welding and common joints | No. 6–8 | Balanced access and coverage for many setups |
| Wide joints, larger parts, longer stickout | No. 8–12, often with a gas lens | Broader coverage; more bulk and potentially more gas use |
These are starting points, not fixed rules. Material thickness alone does not determine cup size. A thin stainless tube may need a generous, steady gas envelope because its backside and heat tint matter; a thicker steel bracket in a sheltered position may weld cleanly with a smaller cup.
Set gas flow for the cup and conditions
For many indoor TIG jobs with argon, roughly 10–20 cubic feet per hour (CFH) is a practical starting range. Begin near 15 CFH, then test on scrap using the same torch position and joint. A larger cup or gas lens may work well at the same flow, but flow requirements depend on cup design, torch distance, gas delivery, and the work environment.
More flow is not always better. Excessive flow can create turbulence that draws air into the shielding envelope, causing contamination even though the meter shows a higher number. Too little flow, a clogged gas passage, or a leaking fitting can also leave the weld exposed. If a clean-looking bead turns gray or black, check leaks and drafts, cup damage, stickout, torch angle, and flow before simply turning up the regulator.
Use an argon flowmeter or regulator suited to your setup; a TIG argon flowmeter regulator can make adjustments more repeatable. Keep the cylinder secured and use fittings rated for the gas system.
Check coverage with a test weld
Run a short bead on scrap from the same material, using the intended joint position. Watch for discoloration and porosity, but also inspect the bead after cleaning: surface appearance alone does not reveal every shielding problem. On stainless steel, heavy straw, blue, gray, or black heat tint can signal excessive oxidation; on other alloys, judge the result using the material’s requirements and procedure.
Keep the cup close without touching the work, and maintain a steady torch angle. A common working gap is around 1/8 to 1/4 inch, though access and process needs vary. A large cup held too far away may shield worse than a smaller cup held at a consistent, close distance. Test where drafts are likely to reach the joint, not only in a sheltered spot on the bench.
Choose cup type, not just diameter
Standard ceramic cups are inexpensive and adequate for many routine jobs. They are a sensible choice for indoor welding with modest stickout and straightforward access. Ceramic can chip if knocked against the work or dropped, so inspect it before welding; cracks and chipped edges can disrupt gas flow.
A gas lens uses a screen assembly to straighten gas flow. It can help with longer tungsten extension, more even coverage, and some awkward positions, but it costs more and adds parts to inspect and keep clean. If you often weld tubing, stainless, or joints requiring extra stickout, compare TIG gas lens kits with cups that match your torch. For occasional, accessible mild-steel work, a standard cup is often fine.
Large cups can improve coverage over a broad area, but they are not a cure for wind. Outdoors, even a large cup may fail in a breeze; use a windscreen or move the work indoors. If you need a smaller opening for access, a gas lens and careful torch positioning may give more reliable coverage than increasing flow.
Buy the right size without overbuying
If you are starting from scratch, a small assortment of compatible No. 5, 6, 7, and 8 cups covers many bench jobs. Confirm cup dimensions and thread or fit style against your torch, and note whether the package includes the matching collet body or gas lens. A cup alone may not fit a different consumable system.
Choose based on the tightest joint you regularly weld, then keep one larger cup available for open joints or longer stickout. Replace chipped cups, and clean gas-lens screens when contamination builds up. The right setup is the one that reaches the joint comfortably and produces consistent coverage at a sensible gas flow—not simply the largest cup on the shelf.