TIG Filler Rod Sizes and Amperage: A Selection Chart
By MIG/TIG/Stick Welders & Plasma Cutters | USA Weld – HTP ... | Published: 2026-10-16
Category: How-to Guides
Match TIG filler rod diameter to your amperage and base metal thickness. A practical step-by-step guide covering ER70S-6, 308L, and 5356 rods.
Quick Answer
Choose your TIG filler rod diameter based on the amperage you are running and the thickness of the base metal. For steel between 1/16 and 1/8 inch, use 1/16-inch ER70S-6 rod at 80-120 amps. For thinner material, drop to 0.045-inch rod and 40-80 amps. For thicker sections above 1/8 inch, step up to 3/32-inch rod and 120-180 amps. Match the rod alloy to the base metal: ER70S-6 for mild steel, 308L for stainless, and 5356 for aluminum.
Why Amperage and Rod Diameter Must Match
The filler rod must melt at roughly the same rate the base metal puddle forms. If the rod is too thin for your amperage, it melts instantly and balls up before you can dip it. If the rod is too thick, it cools the puddle and you lose penetration. The chart below gives starting points for common steel thicknesses. Always test on scrap before welding a critical joint.
For a 1/16-inch rod, run 60-100 amps on steel. For 3/32-inch rod, run 100-160 amps. For 1/8-inch rod, run 150-220 amps. These ranges assume a standard V-groove butt joint or T-joint on mild steel. Aluminum and stainless shift these numbers slightly because of their different thermal conductivity.
- 0.045-inch rod: 40-80 amps, up to 1/16-inch steel
- 1/16-inch rod: 60-100 amps, 1/16 to 1/8-inch steel
- 3/32-inch rod: 100-160 amps, 1/8 to 3/16-inch steel
- 1/8-inch rod: 150-220 amps, 3/16-inch and thicker steel
Selecting the Right Filler Alloy
ER70S-6 is the standard mild steel TIG filler. It contains higher silicon and manganese than ER70S-2, which improves puddle fluidity and helps prevent porosity on dirty or rusty steel. For stainless steel, 308L covers 304, 304L, 308, and 308L base metals. For aluminum, 5356 is stronger and more corrosion-resistant than 4043, but 4043 flows better on castings and thin sheet. Use 5356 for 5052, 6061, and 6063 aluminum.
- Mild steel: ER70S-6 for general purpose, ER70S-2 for clean, tight fits
- Stainless: 308L for 300-series, 309L for dissimilar joints
- Aluminum: 5356 for structural strength, 4043 for castings and thin sheet
How to Read the Chart for Your Job
Measure the thickness of the base metal at the joint. Find that thickness on the left side of the chart. Read across to the amperage range, then down to the recommended rod diameter. For example, 1/8-inch steel calls for 120-180 amps and 3/32-inch rod. If you are welding a root pass, drop one rod size smaller than the chart recommends to get better penetration without burn-through.
If your machine maxes out below the recommended amperage, use a smaller rod and make multiple passes. If your machine runs hotter than the chart, use a larger rod or increase travel speed. Always check the duty cycle of your torch at the amperage you plan to use.
Step-by-Step Selection Process
- Measure the base metal thickness: Use a caliper or tape measure at the joint. For a butt joint, measure the thickness of one plate. For a T-joint, measure the thickness of the vertical plate. Common mistake: guessing thickness. A 1/16-inch difference changes the rod size.
- Identify the base metal alloy: Mild steel, stainless, or aluminum. This determines the filler classification: ER70S-6, 308L, or 5356. Checkpoint: if you are unsure, a magnet sticks to mild steel but not to most stainless or aluminum.
- Find the amperage range for your thickness: Use the chart above. For 1/8-inch steel, start at 120 amps. For 1/16-inch steel, start at 80 amps. Adjust up or down based on your travel speed and joint fit. Common mistake: setting amperage too high for the rod diameter, which causes the rod to melt before it reaches the puddle.
- Select the rod diameter: Match the rod to the amperage. 1/16-inch rod for 60-100 amps, 3/32-inch rod for 100-160 amps, 1/8-inch rod for 150-220 amps. Checkpoint: the rod should melt smoothly into the puddle without forcing or balling up.
- Test on scrap: Run a practice bead on the same thickness and alloy. Watch the puddle. If the rod sticks or the puddle freezes, adjust amperage or rod size. Next step: once the bead is consistent, move to the workpiece.
Product Facts
- ER70S-6 Mild Steel TIG Filler Rod: ER70S-6 mild steel TIG filler rod available in 1/16-inch and 3/32-inch diameters, each 36 inches long, in 2 lb. or 10 lb. packages. These two diameters cover the most common steel thicknesses from 1/16 to 3/16 inch, so you can match the rod to your amperage without buying a full assortment.
- Heat Shield, Large Diameter: Large diameter heat shield designed for 9 Series air-cooled and 20 Series water-cooled TIG torches. When you run higher amperage for thicker steel, the torch head takes more heat. This shield guards the torch head and helps it last longer.
