TIG Filler Rod Buying Guide: Steel, Stainless and Aluminum

Match TIG filler rod to the base metal first: ER70S-2 or ER70S-6 style rod for mild steel, 308L for 304 stainless and 316L for 316, and 4043 or 5356 for aluminum. Then choose a diameter that roughly matches the material thickness, and keep the rod clean. For any work with a required procedure, the procedure decides the rod, not this guide.

Start from the base metal, not the rod

Filler rod is a separate consumable from the tungsten and the cup, and the main question it answers is what metal it must join. TIG welding uses filler on nearly every joint except thin material that can be fused without it. The rod is hand-fed into the pool, so the rod you choose affects the bead, the color and the strength.

The rod classification is printed on the packaging and on a tag or the rod itself. Read it before you buy, and buy from a supplier who lists the classification in full. Rod that is identified only as “steel” or “stainless” leaves you guessing. Our TIG consumable kits guide covers cups, collets and gas lenses, and tungsten types compared covers the electrode.

Mild steel

One technical guide names ER70S-2 and ER70S-6 as the most common choices for mild steel, and describes ER70S-2 as particularly common in motorsport fabrication because it handles thin sheet and tubing well. Both are widely sold. The guide does not explain how they differ, so check the maker's data sheets for the differences in the chemistry and for any guidance on surface condition.

Chromoly and other alloy steels have their own filler recommendations. The same guide says matching chromoly filler is not required unless the assembly will be post-weld heat-treated, and suggests ER70S-2 or ER80S-D2 for most work. If you work with alloy tubing for load-bearing parts, follow the design requirements or consult the manufacturer, not a general article.

Stainless steel

The usual rule is to match the rod to the stainless grade. The technical guide pairs 308L with 304 stainless and 316L with 316 stainless. Check your base metal. If you are not sure of the grade, stainless of unknown origin is not a good place to guess. Ask the seller or test it before choosing a rod.

The guide also notes that stainless can sometimes be fusion-welded without filler where the fit-up is excellent, the metal is thin and the joint is lightly loaded. Treat that as a possibility, not a default, since filler helps with fit-up gaps and weld profile. Keep stainless tools and brushes separate from those used on carbon steel; our wire brush guide and how to weld stainless steel go further.

Aluminum: 4043 versus 5356

These are the two main aluminum rods, and the choice depends on the base alloy and the use. Per the same guide:

• 4043 contains roughly 5 percent silicon, which helps the pool flow. It is suggested for beginners, for appearance and for parts that see sustained heat, and is often chosen for 6xxx alloys for ease of welding and crack resistance.
• 5356 contains roughly 5 percent magnesium and gives higher shear strength than 4043. It can be a little harder to weld cleanly. It may be chosen for strength, for anodized color match or for magnesium-bearing base metals, and is generally avoided for parts that see sustained elevated temperatures because of the risk of stress corrosion cracking.

Cast aluminum is a special case because the alloy is often unknown. The guide notes that 300-series castings usually suit 4043 and 5xx.x castings suit 5356, but cautions that exact alloys are often unknown. If you are not sure, ask a metal supplier or look for markings on the part. Our aluminum welding guide covers machine setup and technique.

Choosing a diameter

The general rule is to roughly match the rod diameter to the material thickness, and the guide says the final choice largely comes down to preference. Your torch, the current you run and your hand speed matter, too. Check your machine manual for suggested pairings with tungsten size.

Cleaning and storing rod

Rod can pick up oils, dirt and oxidation during manufacture and shipping. The technical guide recommends wiping rods with acetone before welding, and notes that many welders cut rods in half because a metre-long rod can make feeding less stable. Follow the safety instructions for any solvent you use, and keep it away from sparks and flames.

Store rod in its tube or a closed container, labelled by classification, in a dry place. Our tool storage guide has ideas. If a rod loses its identification, do not guess; set it aside and buy a labelled replacement.

Buying checklist and common slips

• Confirm the base metal, and for stainless confirm the grade, before choosing a rod.
• Check that the full classification is printed on the pack or tag, not only a general description.
• Buy a diameter close to the material thickness, and a second size if you weld a range of thicknesses.
• Keep each classification in its own labelled tube so that rods never get mixed.
• Do not substitute a rod from a different family because it is on hand; it can change the weld and the color.
• Keep a short length of every rod you buy with its label until you have used the whole batch.

A common slip is buying a large quantity of one rod before trying it. Buying a small quantity of each of the two or three rods you actually use is a smaller commitment than a shelf of the wrong one. If you are new to TIG, the machine matters as much as the rod, and our budget TIG welder guide compares options.