Filler Rod — What It Is and Why It Matters
A filler rod is a length of bare metal wire manually fed into the weld pool during TIG welding and oxy-fuel welding to add material to the joint. Unlike MIG wire (which feeds automatically) or stick electrodes (which carry the arc), TIG filler rods are fed by the welder's off-hand and do not carry current.
Filler rod selection must match the base metal. Common designations include ER70S-6 for mild steel, ER308L for 304 stainless steel, ER309L for dissimilar stainless-to-carbon joints, ER4043 and ER5356 for aluminum, and ERCuSi-A (silicon bronze) for decorative and dissimilar metal work.
Rod diameter is selected based on material thickness — typically matching or slightly smaller than the base material thickness. Standard lengths are 36" for steel and stainless rods, and 36" for aluminum rods. Proper rod storage matters — keep them clean, dry, and in the original tube to prevent contamination that causes porosity.
Frequently Asked Questions
What filler rod do I use for mild steel TIG welding?
ER70S-6 is the standard choice for mild steel TIG welding. The "70" indicates 70,000 PSI tensile strength, "S" means solid wire, and "-6" indicates higher silicon and manganese content for better wetting and deoxidation. It produces clean, strong welds on A36 and similar steels.
What size filler rod should I use?
A common rule of thumb is to match the filler rod diameter to the material thickness or go slightly thinner. For 1/8" steel, use 1/8" or 3/32" rod. For thin material (1/16" and under), use 1/16" rod. Thinner rods melt more easily, giving better puddle control on light-gauge work.