Mig welding wire: ER70S-6 decoded, which diameter, and which spool fits your machine
What ER70S-6 means and why it beats S-3 on rusty steel, which diameter for which thickness, and whether a 2 lb or 10 lb spool fits your mig welder.
Buying mig wire is three decisions: the grade, the diameter and the spool. The grade is nearly always the same answer. The spool is the one people get wrong, because wire makers rarely say how wide their spools are.
For mild steel on a home mig welder, buy ER70S-6 in the diameter your machine lists, usually .030 inch. Every home machine manual we read takes both 4 inch spools (the 2 lb size) and 8 inch spools (10 to 11 lb), sometimes with an adapter. None mentions the 33 lb, 12 inch size.
ER70S-6 or ER70S-3
The last digit is about deoxidizers, which let the wire cope with mill scale and rust.
| Maker | What it says |
|---|---|
| Lincoln | L-56 (S-6): high manganese and silicon deoxidizers tolerate medium to heavy mill scale. L-50 (S-3): moderate levels for clean to light mill scale |
| Hobart | HB-28 (S-6): best choice for rusty and oily plates, preferred over ER70S-3 |
| Miller | Use ER70S-3 for all-purpose welding and ER70S-6 when more deoxidizers are needed for dirty or rusty steel |
Lincoln sells its S-3 wire, L-50, only in 33 lb spools and larger, and every small spool we checked was S-6. Clean the joint anyway; deoxidizers are not a substitute for bare metal.
Which diameter
From Miller’s automotive guide:
| Wire | Thickness Miller lists it for |
|---|---|
| .023 to .024 in | Up to 1/16 in |
| .030 in | 20 gauge to 1/8 in |
| .035 in | 16 gauge to 1/4 in |
The shelf sizes vary slightly: .023 on some brands is .024 on Hobart and .025 on Lincoln. The contact tip and drive roll groove must match the wire, and the wire must be in your machine’s listed range. Settings for each diameter start from the chart inside the machine’s door (six compared in the mig welder settings chart); the welding amps chart explains why mig charts use voltage and wire speed, not amps.
Source: Miller, mig basics for automotive repair.
Will the spool fit your machine
From each machine’s manual or spec sheet, checked 2026-09-27:
| Machine | 4 in spool | 8 in spool | What the manual says |
|---|---|---|---|
| Lincoln POWER MIG 140 MP | Yes | Yes | For 4 inch spools, the hub adapter must be removed |
| Lincoln Easy-MIG 140 | Yes | Yes | Includes a spindle adapter for 8 inch spools |
| Hobart Handler 140 | Yes | Yes | Hub accommodates 4 or 8 inch; adapter for 8 inch only |
| Hobart Handler 210 MVP | Yes | Yes | Adapter used with 8 inch spool only |
| Millermatic 141 and 211 | Yes | Yes | Separate steps for 8 and 4 inch, with adapter and retaining ring |
| YesWelder MIG-205DS | Yes | Yes | Remove the 8 inch spindle adapter for 4 inch spools |
| Eastwood MIG 180 | Yes | Yes | Pre-installed 8 inch adapter; remove it for 4 inch |
Keep the adapter that came with the machine. It is what lets one hub take both sizes.
Which weight is which width? Few wire makers say. ARCCAPTAIN publishes 100 mm for its 2 lb spool and YesWelder 8 inch for its 10 lb spool. Hobart, Lincoln, Harris, Forney and Blue Demon publish weights but not spool diameters. Where a width is given, by those two makers or by the distributor Airgas for Hobart’s 10 lb and Harris’s 11 lb spools, 2 lb means 4 inch and 10 to 11 lb means 8 inch. Check the listing’s photos against your hub before buying a brand for the first time.
The gas it expects
Lincoln lists L-56 for 100 percent CO2, 75 to 95 percent argon with CO2, or argon with 2 to 5 percent oxygen, on DC electrode positive. Hobart lists HB-28 for CO2 or 75 to 92 percent argon with CO2. Lincoln’s parameter table is for CO2, and it says to reduce voltage by 1 to 2 volts when running 75/25. Which gas to buy is in mig welding gas.
Keeping wire from rusting
- Store it in its original, intact packaging (Hobart), between 40 and 120 F, at no more than 80 percent humidity.
- Let wire from a cold garage come within 10 F of the room before opening, so it does not sweat.
- Do not add wire cleaners or aftermarket lubricants to the feed (Hobart).
- Wire on plastic spools should not be heated above 150 F (Lincoln).
Source: Hobart filler metal storage guidelines.
Spools that matched their part numbers
Checked on 2026-09-27, buyable, and matched to the maker’s part number:
| Wire | Spool | Listing |
|---|---|---|
| Hobart ER70S-6, .030 | 2 lb (H305406-R19) | Hobart |
| Hobart ER70S-6, .030 | 10 lb (H305406-R22) | Hobart |
| Hobart ER70S-6, .035 | 10 lb | Hobart |
| Forney ER70S-6, .030 | 10 lb (42286) | Forney |
| Blue Demon ER70S6, .030 | 11 lb | Blue Demon |
We found no Lincoln L-56 listing whose size and weight both matched Lincoln’s part numbers: one 2 lb listing names part ED030631 (.030) but says .025 in its title. Harris had no buy box.
For a gasless machine, the wire is different; see flux core wire. Choosing the machine is in mig welders.
Frequently asked questions
Is .030 or .035 mig wire better?
Miller calls .030 inch a good all-around choice. Its automotive guide gives .030 for 20 gauge to 1/8 inch and .035 for 16 gauge to 1/4 inch. Your machine's chart and contact tips must match whichever you buy.
Will a 33 lb spool fit my mig welder?
None of the home machine manuals we read mentions a 12 inch or 33 lb spool. Lincoln, Hobart, Miller, YesWelder and Eastwood manuals all describe 4 inch and 8 inch spools.
Does mig wire go bad?
It can rust. Hobart says to store wire in its original intact packaging, between 40 and 120 F at no more than 80 percent humidity, and to let cold wire reach room temperature before opening it.
What does ER70S-6 mean?
Hobart: ER is an electrode or rod, 70 is 70,000 psi tensile strength, S is solid wire, and 6 reflects the chemistry and shielding gas requirements. The 6 carries the most deoxidizers of the common grades, for mill scale and rust.