Most people choose filler metal by asking what the shop has in stock. That works until the weld cracks, the bead sits on top instead of fusing, or a joint that looked fine fails under load.
Four questions settle nearly every selection: what metal you are joining, how thick it is, which process you are running, and where the work happens. Get those straight, and the box almost picks itself.
The numbers on the box mean something
AWS classifications look like part numbers and are actually a specification.
On a stick electrode, E7018 breaks down cleanly. E means electrode. The first two digits give minimum tensile strength in thousands of pounds per square inch, so 70 means 70,000 psi. The third digit describes which positions the rod runs in, with 1 meaning all positions. The fourth indicates coating type and preferred current.
Wire follows similar logic. ER70S-6 uses ER for electrode or rod, 70 for the same tensile figure, S for solid, and the trailing number for composition. Once the pattern is familiar, the label tells you strength and working conditions before anyone at the counter says a word.
Stick electrodes: four cover most work
Stick welding stays popular for repair, structural work, and anywhere a gas bottle is inconvenient.
**E6010** runs on DC, digs deep, and cuts through rust, paint, and mill scale better than anything else here. It is the standard for root passes and pipe, and it is unforgiving of a beginner’s hand.
**E6011** behaves much like 6010 but also runs on AC, which matters with an older transformer machine. Farm and field repair leans on it.
**E6013** has a softer arc and lighter penetration, making it the friendliest rod for thin material and general fabrication on clean metal.
**E7018** is the low-hydrogen rod and produces the strongest, most ductile welds of the four. It wants clean metal, a tight arc, and material thick enough to justify it. Structural work runs on it.
The pattern worth remembering is that penetration and cleanliness trade against each other. Rusty metal points toward 6010 or 6011. Clean metal and strength requirements point toward 7018.
Low-hydrogen rods need dry storage
This one causes failures that get blamed on technique.
The coating on a 7018 electrode absorbs moisture from the air, and that moisture becomes hydrogen in the weld. Trapped hydrogen causes cracking that can appear hours or days after the work is finished, which is why it is called delayed cracking.
Keep them in a sealed container or a rod oven rather than an open box on a shelf. A rod left out in a humid garage is a different product than the one that left the factory. This matters more on code work than on a gate repair, though the mechanism is identical.
MIG wire and the gas behind it
Solid wire is the most common choice for shop work on mild steel, and the gas is half the decision.
ER70S-6 is the general-purpose answer. It carries more deoxidizers than leaner wires, so it tolerates some mill scale rather than demanding spotless metal. For most carbon steel fabrication, it is what you want.
Diameter follows thickness. A .030 wire suits thin sheet, .035 handles general shop work, and .045 moves more metal on heavier sections. Heavy wire on thin material burns through, and thin wire on heavy plate takes forever and risks cold lap. Our welding supplies in Las Vegas counter stocks the common diameters rather than making you order them.
Shielding gas changes the result more than people expect. A 75 percent argon and 25 percent carbon dioxide blend gives a smoother arc, less spatter, and a better bead, which suits thin material and visible welds. Straight carbon dioxide penetrates deeper and costs less, at the price of spatter and a rougher bead.
Flux-cored when the wind is a problem
Shielding gas does not survive a breeze, which is why outdoor work goes a different direction.
Self-shielded flux-cored wire such as E71T-11 generates its own shielding from the flux inside, so it runs without a bottle and holds up outdoors where a MIG gun would produce porous welds. That makes it the practical choice for field repair and site work.
Gas-shielded flux-cored wire is different, pairing a flux core with external shielding gas for high deposition on heavy material in a shop. Both leave slag that needs chipping, which solid wire does not.
Aluminum and stainless follow different rules
Filler selection gets less forgiving once you leave carbon steel.
For aluminum, the choice usually comes down to two rods. ER4043 contains silicon, flows more easily, and resists cracking, which makes it a common pick for 6061 and general repair. ER5356 contains magnesium, offers higher strength, feeds better through a spool gun, and holds color better if the piece gets anodized. Both run under 100 percent argon. When sourcing aluminum materials for a fabrication project, experienced Aluminum Tube Suppliers can also help you select tubing that matches your welding and application requirements.
For stainless, match the filler to the alloy. ER308L is the usual answer for 304, ER316L for 316, and ER309L when joining stainless to carbon steel, since it handles dilution between two chemistries. The L indicates low carbon, which reduces corrosion risk at the weld.
Match the filler to the base metal
The most common selection error is choosing filler by habit rather than by what is on the table.
What you are welding is not always obvious from appearance, and it decides the filler. Our guide to common metals used in welding and fabrication covers how the main families behave under heat.
Thickness shapes it too, since heavy sections need a filler and process capable of carrying load while thin material needs restraint. Our post on how thick your steel needs to be works through that side.
Fit-up matters more than filler choice on a bad joint, because a square, clean cut closes gaps no electrode compensates for. That is what saw cutting delivers on structural shapes.
Frequently asked questions
1) Can I use 7018 on rusty metal?
You can strike an arc, but not expect a sound weld. Low-hydrogen rods want clean base metal. Grind to bright metal first, or run a 6010 or 6011 instead.
2) What is the difference between ER70S-6 and ER70S-3?
Deoxidizer content. The S-6 carries more silicon and manganese, which lets it tolerate mill scale and light surface contamination. The S-3 runs well on clean material and is often cheaper.
3) Do I need gas with flux-cored wire?
It depends on the wire. Self-shielded wire generates its own shielding and needs no bottle. Gas-shielded flux-cored wire requires one, so check the classification before setting up.
4) Why does my aluminum weld keep cracking?
Aluminum is sensitive to filler selection and heat input. Confirm the alloy and match the rod to it, since the wrong filler on a crack-sensitive alloy cracks regardless of technique.
5) How much filler should I buy for a job?
More than you calculate. Consumables get burned on setup, test coupons, and restarts, and running out mid-job costs more in downtime than a spare spool costs on the shelf.
Conclusion
Filler selection comes down to four inputs: what the base metal is, how thick it is, which process you are running, and whether the work happens indoors or out. The classification on the box answers the rest once you know how to read it.
Curtis Steel & Aluminum has been a family business in Las Vegas for more than five decades, carrying consumables and safety gear alongside the metal itself. The Wynn Road showroom is open weekdays and Saturday mornings.
Reach the counter at 702.952.3000, or request a quote with the details of what you are joining and we will point you to the right consumable.