A #7 or #8 cup with a gas lens collet body is the best general-purpose setup for most TIG work. The gas lens smooths argon flow from turbulent to laminar, giving you better gas coverage at longer tungsten stickout. For tight joints, drop to a #5 or #6. For critical gas coverage on stainless and titanium, go to a #10 or #12 with a jumbo gas lens.
Cup size, collet body type, and gas flow rate work together to determine how well your shielding gas protects the weld. A bigger cup with a gas lens and higher flow rate gives the best coverage. A smaller cup without a gas lens fits into tighter spaces but compromises coverage. Every setup is a tradeoff between access and shielding quality.
Understanding Cup Sizes
TIG cups are numbered by their inside diameter in sixteenths of an inch. A #8 cup has a 8/16" (1/2") inside diameter. A #12 cup has a 12/16" (3/4") diameter.
| Cup Number | Inside Diameter | Gas Flow (CFH) | Best For |
|---|---|---|---|
| #4 | 1/4" (6.4 mm) | 8-12 | Very tight access, inside corners, small parts |
| #5 | 5/16" (7.9 mm) | 10-15 | Tight joints, pipe root passes, restricted spaces |
| #6 | 3/8" (9.5 mm) | 12-18 | Pipe welding, moderate access restrictions |
| #7 | 7/16" (11.1 mm) | 15-20 | General purpose, good balance of access and coverage |
| #8 | 1/2" (12.7 mm) | 18-25 | General purpose, slightly better coverage than #7 |
| #10 | 5/8" (15.9 mm) | 20-30 | Stainless, titanium, improved coverage on flat joints |
| #12 | 3/4" (19.1 mm) | 25-35 | Maximum coverage, critical applications, aluminum |
| #14 | 7/8" (22.2 mm) | 30-40 | Specialty, trailing shield replacement on flat work |
Larger cups consume more argon. A #12 cup at 30 CFH uses about three times the gas of a #5 cup at 10 CFH. On a standard 80 CF argon cylinder, the difference is significant over a day of welding.
Cup Materials
Alumina Ceramic (Pink/Tan)
Standard ceramic cups that come with most TIG torches. Inexpensive, adequate for most work. They crack if dropped or knocked against the workpiece. The ceramic is porous enough that it can absorb moisture in humid environments. Keep spare cups on hand.
Fused Quartz (Clear)
Clear quartz cups let you see the tungsten and the gas envelope during welding. Useful for training and for dialing in new setups because you can see the gas flow pattern. More heat-resistant than alumina. More expensive and still fragile.
Pyrex (Clear)
Similar visibility benefits to quartz at a lower price. Less heat-resistant than fused quartz. Good for low-to-moderate amperage work.
Ceramic with Metal Jacket
Ceramic cups wrapped in a metal sleeve for impact protection. They survive bumps and drops that would crack a bare ceramic cup. The metal jacket adds some weight but dramatically extends cup life in rough shop environments.
Standard Collet Body vs. Gas Lens
This is the single biggest upgrade you can make to a TIG torch. The difference in gas coverage between a standard collet body and a gas lens is dramatic.
Standard Collet Body
The collet body that ships with most TIG torches has a few small holes that direct argon into the cup. The gas exits the cup in a turbulent, cone-shaped pattern that breaks up quickly. Effective gas coverage extends about 1/4" beyond the cup opening.
Standard collet body limitations:
- Tungsten stickout limited to 1/4" (tungsten tip must be close to the cup exit)
- Gas coverage is narrow and turbulent
- Sensitive to crossdrafts
- Coverage deteriorates rapidly with distance from the cup
- Adequate for basic mild steel work
Gas Lens Collet Body
A gas lens replaces the standard collet body with a unit containing a fine mesh stainless steel screen (or multiple screens). This screen breaks the gas flow into hundreds of tiny parallel streams, converting turbulent flow to smooth laminar flow.
Gas lens advantages:
- Tungsten stickout up to 3/4" without losing coverage
- Wider, smoother gas envelope
- Better protection of the cooling HAZ
- More resistant to mild drafts
- Extended stickout lets you reach into tight joints and corners
- Visible improvement in weld color on stainless and titanium
Gas lens disadvantages:
- More expensive than standard collet bodies
- The mesh screen can clog with spatter or debris
- Larger diameter than standard, limits access in very tight spaces
- Requires matching cups (standard cups may not fit gas lens bodies)
Visible Difference in Gas Coverage
With a standard collet body and a clear cup, you can see the gas flow exits the cup as a cone that fans out and dissipates within an inch. With a gas lens and clear cup, the gas exits as a smooth, visible column that stays coherent for 2-3 inches beyond the cup opening.
On stainless steel, this difference shows up as weld color. A standard collet body might produce a blue or brown heat tint at the weld toes where gas coverage is marginal. A gas lens on the same joint at the same flow rate produces a silver or light straw color because the coverage extends further.
Jumbo Gas Lens Setups
A jumbo (or large-format) gas lens uses an oversized screen assembly with a matching large-diameter cup (#12 to #20). These setups provide maximum gas coverage for critical applications.
When to Use Jumbo Gas Lens
- Titanium welding where every square inch of the HAZ must be shielded
- Stainless pipe and tubing where silver welds are required
- Aluminum work where porosity from gas contamination is a recurring problem
- Replacing a trailing shield on flat or horizontal work (the massive gas envelope covers the cooling zone behind the arc)
- Walking the cup on pipe where the large cup rolls smoothly and provides excellent coverage
Jumbo Gas Lens Setup
- Install the jumbo gas lens body into the torch head (same thread as standard collet body)
- Insert the matching collet for your tungsten diameter
- Thread on the jumbo cup (#12, #14, or larger depending on the setup)
- Set gas flow to 25-40 CFH depending on cup size
- Extend tungsten stickout to 1/2" to 3/4"
The large cup diameter makes jumbo setups unsuitable for tight access work. You can’t fit a #14 cup into the root of a V-groove or an inside corner on a small part. Jumbo setups excel on open joints, pipe exteriors, and flat/horizontal work.
For walking the cup technique with large cups, see walking the cup.
Gas Flow Rate Guidelines
Flow rate depends on cup size, collet body type, and working conditions. Too little gas leaves the weld unprotected. Too much gas creates turbulence that pulls air into the gas envelope.
| Cup Size | Standard Collet (CFH) | Gas Lens (CFH) | Jumbo Gas Lens (CFH) |
|---|---|---|---|
| #4 | 8-12 | 10-14 | N/A |
| #5 | 10-14 | 12-16 | N/A |
| #6 | 12-16 | 14-18 | N/A |
| #7 | 14-18 | 16-20 | N/A |
| #8 | 16-22 | 18-24 | N/A |
| #10 | 20-26 | 22-28 | N/A |
| #12 | N/A | 25-32 | 28-35 |
| #14 | N/A | N/A | 32-40 |
In drafty conditions: Add 5-10 CFH above the recommended range. Better yet, block the draft with welding screens or cardboard. No amount of gas flow overcomes a steady breeze blowing across the joint.
Too much flow is real. Cranking the flowmeter to 40+ CFH on a small cup creates venturi-effect turbulence inside the cup that actually pulls air into the gas stream. The optimal flow rate is the lowest rate that provides complete coverage. Test by watching for consistent weld color on stainless or titanium.
Choosing the Right Setup for Your Work
Mild Steel General Fabrication
Standard collet body with #7 or #8 ceramic cup at 15-20 CFH. Steel is forgiving on gas coverage. A standard setup produces clean welds without any issues. Upgrading to a gas lens improves color but isn’t required.
Stainless Steel
Gas lens with #8 or #10 cup at 20-28 CFH. The improved gas coverage produces better weld color and reduces oxidation in the HAZ. For food-grade and sanitary stainless, a gas lens is effectively required to achieve acceptable weld color.
Aluminum
Gas lens with #8-#12 cup at 20-30 CFH. Aluminum’s tendency toward porosity makes good gas coverage important. The longer tungsten stickout that a gas lens allows is helpful for reaching into aluminum joint geometries.
Titanium
Jumbo gas lens with #12+ cup at 30+ CFH, plus trailing shield or chamber. Titanium demands the best possible gas coverage. See TIG welding titanium for full shielding requirements.
Pipe and Tube
Gas lens with #5-#7 cup for root passes in tight spaces. Standard or gas lens with #6-#8 for cap passes on pipe exteriors. The smaller cup fits through pipe bevels and around tight-radius tube joints.
Thin Sheet Metal
Gas lens with #6-#8 cup. The extended stickout from a gas lens is valuable on thin material because it gives you a clear view of the puddle. On bench work, a #8 with gas lens is the most versatile thin-material setup.
Common Cup and Gas Lens Problems
Cup Cracking
Ceramic cups crack from thermal shock (touching cold metal with a hot cup) and mechanical impact. Keep spares on hand. When a cup cracks, gas escapes through the crack and shielding fails on that side of the weld. Replace cracked cups immediately.
Gas Lens Screen Clogging
Spatter, condensation, and airborne debris can clog the fine mesh screens in a gas lens. Clean by soaking in acetone and blowing compressed air through the screen. If flow is visibly reduced even after cleaning, replace the gas lens.
Inconsistent Gas Coverage
If weld color varies from one side to the other (e.g., straw on the left, blue on the right), check for:
- Cracked cup allowing gas to leak on one side
- Bent or damaged gas lens screen
- Tungsten not centered in the cup
- Crossdraft from one direction
Tungsten Too Far Extended
Even with a gas lens, extending the tungsten more than 1" beyond the cup pushes the arc outside the effective gas envelope. Keep stickout under 3/4" for gas lens setups. With a standard collet body, keep it under 1/4".
Torch Compatibility
Cup and gas lens components are torch-series specific. The most common TIG torch series and their cup/gas lens compatibility:
- 9/20 series (air-cooled, 125-200A): Small-format cups and gas lenses. Limited to #10 cup maximum.
- 17 series (air-cooled, 150A): Standard cups up to #8. Gas lens available but less common.
- 18 series (water-cooled, 350A): Full range of standard cups and gas lenses. Supports jumbo gas lens.
- 26 series (air-cooled, 200A): Same cup/gas lens format as 17 series.
Always match the gas lens, collet, and cup to your specific torch series. Components from different series don’t interchange even if they look similar. Check part numbers against the torch manufacturer’s compatibility chart before ordering.