If you're standing in front of your welder wondering whether to load ER70S-6 or E71T-GS, here's the short answer: use ER70S-6 when you have shielding gas and want clean, multi-pass welds; use E71T-GS when you're working outdoors, don't have gas, or need a fast single-pass repair. That's the core of it. Everything below explains the why so you make the right call for every job.
ER70S-6 is your workhorse for shop welding with shielding gas: cleaner beads, multi-pass capable, better for thin material. E71T-GS is your go-to for outdoors, no-gas situations, or quick repairs where portability matters more than cosmetics. Both are classified for 70,000 psi minimum tensile deposit. The key differences are process requirements, polarity, and what you can and can't do with the weld afterward.
What the Classifications Actually Mean
The wire names aren't random. AWS classification language tells you exactly what you're working with, and knowing how to read the code saves time when you're ordering or spec-ing a job.
E = electrode & filler rod | R = can be used as a rod | 70 = 70,000 psi minimum tensile deposit | S = solid wire | 6 = higher manganese and silicon deoxidizer content. That elevated Si/Mn is why ER70S-6 tolerates light mill scale and surface oxidation; the deoxidizers do the cleanup work so your welds don't come out porous on slightly dirty base metal.
E = electrode | 7 = 70,000 psi minimum tensile deposit | 1 = all-position capable | T = tubular wire (flux-cored) | GS = single-pass, self-shielded. The flux packed inside the wire core generates its own shielding gas when it burns, with no external cylinder needed. The "GS" designation signals this wire is rated for single-pass work only.
Both wires deposit weld metal with a minimum 70,000 psi tensile strength rating. What differs is how they get there, what they require to run, and what you can do with the weld afterward.
Gas or No Gas: The Setup Difference
ER70S-6 is a gas-shielded wire; it requires an external shielding gas cylinder. The standard shielding gas for ER70S-6 on mild steel is 75% Argon / 25% CO2 (C25): stable arc, low spatter, good bead appearance. Pure CO2 (C100) also works and costs less, but produces more spatter and a rougher bead.
E71T-GS eliminates the gas requirement entirely. The flux compound packed inside the tubular wire generates shielding when it combusts. No cylinder, no regulator, no gas line. That's why welders reach for it outdoors or on job sites where hauling a cylinder isn't practical.
Never run shielding gas on E71T-GS. External gas disrupts the self-shielding chemistry and degrades weld quality. Self-shielded flux-core and shielding gas are not compatible; pick one or the other based on your wire type.
Side-by-Side Comparison
| Factor | ER70S-6 (Solid MIG) | E71T-GS (Gasless Flux-Core) |
|---|---|---|
| AWS Classification | A5.18 ER70S-6 | A5.20 E71T-GS |
| Shielding Gas | Yes: C25 or CO2 | No: self-shielded |
| Polarity | DCEP (Electrode Positive) | DCEN (Electrode Negative) |
| Multi-Pass | Yes | No: single-pass only |
| Outdoor / Wind | Poor: gas shield disrupted | Good: no gas to disrupt |
| Bead Appearance | Clean, smooth, low spatter | Rougher; slag must be chipped |
| Thin Sheet Metal | Excellent: precise heat control | More difficult: runs hotter |
| Portability | Requires cylinder & regulator | Run anywhere with a MIG machine |
| Best For | Shop fab, auto body, structural | Field repairs, outdoor, single-pass |
Polarity: The Mistake Everyone Makes
This is the most common reason welders get a bad arc when switching between these two wires. They're opposite polarity.
ER70S-6 Polarity
DCEP / Reverse PolarityGun lead connects to the positive terminal. This is the default on most MIG machines, so most welders are already set correctly for solid wire.
E71T-GS Polarity
DCEN / Straight PolarityGun lead connects to the negative terminal. If you switch from ER70S-6 without flipping polarity, you'll get a stubbing, sputtering arc with poor penetration and excessive spatter.
Put a label on your machine: "ER70S-6 = DCEP" and "E71T-GS = DCEN." Most MIG machines have two leads inside the wire feed compartment; swap them to switch polarity. It takes 30 seconds and is the first thing to check when flux-core won't arc cleanly.
Real-World Scenarios: Which Wire Wins
Use ER70S-6. You have gas, you're inside, and you want consistent bead quality. ER70S-6 with C25 gives you the cleanest arc, least spatter cleanup, and the ability to run multi-pass on heavier sections without slag entrapment issues.
Typical setup: .035" wire, C25 gas at 20-25 CFH, DCEP. Dial in wire speed and voltage for your material thickness, then fine-tune from there.
Use E71T-GS. You can't control the wind, you don't want to haul a cylinder, and the repair doesn't need to be pretty; it needs to hold. Self-shielded flux-core was built for exactly this situation.
Remember: E71T-GS is single-pass only. If the joint requires more than one pass of penetration, this isn't the right wire for the job.
Use ER70S-6 in a smaller diameter. For 22 to 18 gauge sheet metal, .023" or .030" ER70S-6 with C25 gives you the heat control you need without burning through. E71T-GS runs hotter and produces a rougher bead that requires more grinding.
Sheet metal work rewards short bursts and tack-and-stitch technique; ER70S-6's stable arc makes this much easier to manage.
Either works; gas wins if you have it. E71T-GS is quick and portable for field tacks. But if a cylinder is practical, ER70S-6 gives you cleaner tacks that are easier to inspect before the final pass crew comes through.
If the structure requires multi-pass fillet or full-pen groove welds by code, ER70S-6 is the correct choice; E71T-GS single-pass rating won't satisfy most WPS requirements.
The Single-Pass Limit: Why It Matters
The "GS" in E71T-GS stands for single-pass, self-shielded. Running a second pass on top of GS slag can trap inclusions in the weld, creating internal defects that don't show on the surface but compromise joint integrity.
Single-Pass OK
Light structural tacks, farm equipment, trailers, brackets, frames, anywhere one pass fills the joint and meets the strength requirement.
Multi-Pass Needed
Heavy structural fab, pipe work, anything with a WPS requiring multiple passes; use ER70S-6 with shielding gas or E71T-1C (multi-pass rated).
Code-Inspected Work
Any work under AWS D1.1 or ASME codes: check your WPS. E71T-GS may not be an approved filler. ER70S-6 or E71T-1C are safer choices.
Thickness Ceiling
E71T-GS is typically practical up to about 3/16" in a single pass on most machines. Beyond that, you're in multi-pass territory and need a different wire.
Copper Bridge ER70S-6 and E71T-GS
Both wires are manufactured by Dingzhou Jinlong Metal Products Co., Ltd., established in 2004, and stocked at our Riverside, CA warehouse. Factory-backed consistency, no middleman markup.
Copper Bridge ER70S-6: Solid MIG Wire
Classified as AWS A5.18 ER70S-6. Available in .023", .030", and .035" diameters. 2 lb, 11 lb, and 33 lb spools. Runs on DCEP with C25 or CO2. Consistent feedability, clean arc, low spatter.
Copper Bridge E71T-GS: Self-Shielded Flux-Core Wire
Classified as AWS A5.20 E71T-GS. Available in .030" and .035" diameters. Runs on DCEN; no shielding gas required. All-position capable for single-pass applications.
Quick Decision Checklist
- Do you have shielding gas? Yes: ER70S-6. No: E71T-GS.
- Welding outdoors in wind? Yes: E71T-GS. No: ER70S-6 preferred.
- Need more than one pass? Yes: ER70S-6 only. No: either works.
- Thin sheet metal under 14 gauge? Yes: ER70S-6 .023" or .030" for better heat control.
- Code-inspected structural weld? Yes: check your WPS. ER70S-6 or E71T-1C are the safer choices.
- Did you flip polarity? ER70S-6 = DCEP. E71T-GS = DCEN. Do this before you strike an arc.
Frequently Asked Questions
Can I use E71T-GS for multi-pass welds?
No. E71T-GS is classified as a single-pass wire; the "GS" designation means single-pass, self-shielded. Running multiple passes on top of GS slag can trap inclusions and create weak, porous welds. For multi-pass work, switch to ER70S-6 with shielding gas, or a multi-pass rated flux-core like E71T-1C.
What polarity does E71T-GS run on?
E71T-GS runs on DCEN (Direct Current Electrode Negative), also called straight polarity. This is the opposite of ER70S-6, which runs DCEP. Forgetting to swap polarity when switching wire types is one of the most common causes of poor arc performance. Most MIG machines default to DCEP and need to be manually switched for self-shielded flux-core.
What shielding gas do I use with ER70S-6?
The standard is 75% Argon / 25% CO2 (C25): stable arc, good bead appearance, low spatter. Pure CO2 (C100) also works and costs less per cubic foot, but produces more spatter. Never use shielding gas with E71T-GS; it disrupts the self-shielding chemistry and degrades weld quality.
Which wire is better for outdoor welding?
E71T-GS. It generates its own shielding from the flux inside the wire, so wind doesn't strip away a gas shield. ER70S-6 requires shielding gas that can be disrupted by even moderate wind; anything above about 5 mph starts causing porosity. If you're welding outdoors without windbreaks, E71T-GS is the right call.
Does wire diameter matter when choosing between these two?
Yes. ER70S-6 is available in .023", .030", .035", and .045": smaller diameters for sheet metal, larger for structural work. E71T-GS is most commonly available in .030" and .035". For light gauge sheet metal, .030" ER70S-6 with shielding gas gives better control than flux-core.
