Choosing the right TIG welding filler rods used to confuse the hell out of me—especially when I was bouncing between aluminum jobs, stainless repairs, and mild steel fabrication all in the same week. One day I’d grab ER70S-2, the next ER308L, and sometimes I’d guess wrong and wonder why my puddle wasn’t wetting in right or why the bead color looked off.
When you’re switching from MIG vs TIG, dealing with different metal thicknesses, or trying to dial in your arc control, the filler rod you choose makes a massive difference. Pick the wrong one, and you can end up with weak welds, cracks, or a bead that just doesn’t bond like it should.
But pick the right filler rod, and everything flows smoother—you get stronger welds, cleaner results, and way less frustration. Stick with me, because in this guide I’ll break down exactly how to choose TIG filler rods the smart way, so every weld you lay down has the strength and quality you’re after.
Image by yeswelder
Why Filler Rod Choice Actually Matters More Than Your Tungsten Grind
Most new guys obsess over torch angle and amperage, but the filler rod is literally the metal that becomes your weld. If it doesn’t match the base material chemically and mechanically, you’re building in weakness from the start. I’ve seen beautiful-looking beads on 6061 aluminum pop apart like a candy bar because somebody left in the Arizona sun—all because the guy grabbed 4043 instead of 5356.
Same thing happens in stainless when you mix a 308 rod with 316 base metal and end up with corrosion pits six months later.
The rod controls strength, corrosion resistance, crack sensitivity, and even color match. Pick wrong and no amount of perfect arc control saves you.
Understanding TIG Filler Rod Designations So They Stop Looking Like License Plates
Every TIG rod sold in the U.S. follows the American Welding Society (AWS) classification. Once you speak the language it’s actually pretty logical.
The most common start with “ER.”
ER = Electrode/Rod (usable in both GTAW and GMAW).
Next come the numbers and letters that tell you exactly what’s in the alloy.
For mild and low-alloy steel: ER70S-2, ER70S-6, etc.
The 70 means minimum 70,000 psi tensile strength in the weld deposit.
S = solid wire.
The last number or letter tells you chemistry and deoxidizers (2 = triple deoxidized and very clean, great for rusty metal; 6 = higher silicon and manganese, flows better on dirty or painted steel).
For stainless: ER308L, ER316L, ER309L
The number is the AISI stainless grade it matches.
L = low carbon (helps prevent carbide precipitation and sensitization).
For aluminum: ER4043 and ER5356 are the big dogs.
4043 = silicon alloyed, very fluid, great for 6XXX series and castings.
5356 = magnesium alloyed, stronger, better color match on 5XXX series.
For nickel alloys, titanium, copper—same idea, just different prefixes.
I keep a laminated AWS filler metal chart taped inside my toolbox door. Takes ten seconds to glance at and saves hours of headache.
Matching Filler Rod to Base Material: The Golden Rule
Rule #1 I teach every new helper: the filler rod should match or slightly overmatch the base metal properties.
Carbon and Low-Alloy Steels
ER70S-2: my go-to for critical welds, rusty plate, or when I want minimum spatter and inclusions.
ER70S-6: everyday structural, heavier mill scale, or when I’m running a little hotter.
Stainless Steel
304/304L base → ER308L
316/316L base → ER316L
Welding 304 to 316 dissimilar → ER309L (over-alloyed on purpose)
Welding carbon steel to stainless → ER309L or ER309MoL
Aluminum
6XXX series (6061, 6063) → either 4043 or 5356 works, but 4043 flows better on thin stuff.
5XXX series (5086, 5454) → 5356 only, higher strength and much better crack resistance.
Cast aluminum → 4043, runs like water into porosity.
Titanium
Commercially pure titanium → ERTi-2
Ti-6Al-4V → ERTi-5
Never mix grades—titanium is unforgiving.
Diameter Selection: Why Rod Size Isn’t One-Size-Fits-All
I stock 1/16″, 3/32″, and 1/8″ in my most-used alloys. Here’s how I pick:
Thin material under 1/8″ thick → 1/16″ rod (easier to feed, less heat buildup).
1/8″ to 3/8″ → 3/32″ is the sweet spot for most shop work.
Over 3/8″ or heavy multipass → 1/8″ lets you add metal faster without cranking amperage sky-high.
Pro move: on really thin stuff I’ll even cut 3/32″ rods in half lengthwise with side cutters so I’m feeding a 3/64″-ish strip. Gives insane control on 0.030″ stainless.
Common Mistakes I See (and Used to Make Myself)
Grabbing whatever rod is already in the torch when switching materials. I’ve turned beautiful 316 pipe into scrap because I forgot to swap from 308L. Now I physically hang the rod tube on the torch holder—out of sight, out of mind doesn’t work here.
Using 4043 on 5083 marine plate. Looks pretty until the weld cracks along the fusion line under vibration. 5356 only for 5XXX over 3% magnesium.
Buying cheap imported rods with no certification. Spent $80 on “ER70S-6” that turned into Swiss cheese from hydrogen porosity. Stick with Lincoln, Hobart, Harris, or ESAB if you want consistent chemistry.
Storing rods in the damp. Aluminum especially sucks moisture out of the air and gives you porous welds. I keep mine in a heated rod oven or at least sealed plastic boxes with desiccant.
Step-by-Step: How I Choose Filler Rod on Every New Job
- Identify base metals (look at the mill cert or at least the stamp on the edge).
- Decide if it’s same-alloy or dissimilar weld.
- Check the service environment (corrosion, high temp, cryogenic, food contact?).
- Pull the AWS filler metal selection guide or my cheat sheet.
- Confirm joint thickness and position (out-of-position needs a stiffer puddle sometimes).
- Grab the rod, snip the tip clean, and double-check the printing on the rod itself.
Takes thirty seconds and saves hours of grinding out bad welds.
Quick Reference Table I Keep on the Shop Wall
| Base Material | Recommended Filler | Backup Choice | Notes |
|---|---|---|---|
| Mild steel | ER70S-2 or ER70S-6 | ER70S-3 | -2 for rusty, -6 for dirty/painted |
| 4130 chrome-moly | ER80S-D2 or ER80S-Ni2 | Must preheat & post-heat | |
| 304/304L stainless | ER308L | Most common stainless rod | |
| 316/316L stainless | ER316L | Moly for pitting resistance | |
| 6061 aluminum | ER4043 or ER5356 | 4043 flows better, 5356 stronger | |
| 5083/5086 aluminum | ER5356 | ER5183 | Never 4043—will crack |
| Commercially pure Ti | ERTi-2 | ||
| Ti-6-4 | ERTi-5 | ||
| Carbon to stainless | ER309L | ER309LSi |
Machine Settings That Play Nice With Different Rods
Stainless 308L/316L: I run straight argon, 1-2% less amperage than mild steel because stainless transfers heat slower. Balance on AC squarewave around 70-75% EN for cleaning.
Aluminum 5356: More amperage than 4043 because it’s stiffer puddle. I bump balance to 80-85% EN on thicker plate.
ER70S-2 on steel: Pure argon, sharp tungsten, 100-120 Hz pulse helps control the puddle on thin stuff.
Cleaning and Prep: Where Most Rod Problems Actually Start
I don’t care if you bought the most expensive rod on the planet—if your base metal or the rod itself is dirty, the weld is trash.
Stainless: wipe with acetone, stainless wire brush only, wear nitrile gloves so skin oil doesn’t contaminate.
Aluminum: fresh stainless brush or dedicated aluminum file right before welding, then acetone wipe.
Titanium: same but add a dedicated Scotch-Brite room—cross-contamination kills titanium welds.
I keep three separate stainless cups on the bench: one for carbon, one for stainless, one for aluminum/titanium. Color-code the handles with heat-shrink so I never mix them.
Final Pro Tip From Twenty Years of Burning Rod
When in doubt, overmatch slightly rather than undermatch. A 309 on 304-to-carbon is always safe. A 5356 on 6061 is always safe. But never the reverse.
You now know exactly what I do every single time I fire up the torch. Match the base metal, respect the service conditions, keep everything surgically clean, and buy quality rod from a reputable supplier. Do that and your TIG welds will be stronger, cleaner, and you’ll sleep better knowing they won’t fail on the job site.
FAQs
Can I use the same filler rod for MIG and TIG?
Yes, if it’s labeled ER (not just R or E). Chemistry is identical. Only difference is MIG rod comes on spools, TIG comes straight in 36″ lengths.
Is ER4043 or ER5356 better for 6061 aluminum?
Both work great. Use 4043 for better fluidity and welding castings or 6XXX heat-treated plate you’re going to re-heat-treat. Use 5356 when you need maximum strength and the weld will stay as-welded.
Do I need a rod oven for TIG rods?
Not mandatory like stick electrodes, but highly recommended for aluminum and low-hydrogen steel rods if you’re in a humid climate. I keep a $120 rod oven running at 250 °F in the corner—cheap insurance.
Why does my stainless weld look gray instead of silver?
Too much heat or oxygen contamination. Lower amperage, increase travel speed, check for draft across the puddle, or add 2-5% helium to argon for better wetting.
Can I weld aluminum with pure argon?
Yes, that’s standard. Helium mixes are only needed for very thick aluminum or automated high-speed welding.