As a new or novice welder, it is tricky to know which is the right size to go for.
In the battle between .030 vs .035 flux core wire, even the most experienced debate what flux core wire to use. I tell you three stories to help you decide and
At the end I'll give you 16 points to bear in mind before you buy.
First let me explain a few fundamentals of flux core so you have a base line of knowledge. Know this already? Breeze though the next five headings.
What is Flux Core Welding Wire?
Flux core wire is one form of welding wire you can use in your MIG welder.
Popular because you can weld without the need for a separate tank of shielding gas. The flux in the center of flux core wire is designed so that when it melts the flux core wire provides filler metal for your weld and the shielding gases to protect your weld.
When is Flux Core Wire Used?
Flux core is often chosen to weld outside where the weather can cause problems with MIG welding.
If it is difficult for you to get to the location,
Or for you to use shielding gas then flux core wire welding is your buddy.
Benefits of Welding with Flux Core Wire?
Flux core is more tolerant of rust and other contaminants although clean steel is always recommended.
Solid wire in contrast demands clean steel.
Flux core is also more tolerant of the skill (or rather lack) of the user.
Using Shielding Gas with Self Shielding Flux Core Wire?
Using separate shielding gas with flux core wire stated and sold as self shielding, will produce problems with your weld.
Because the compounds in the self shielding flux core wire need to and are designed to react with the air to work and protect your weld.
If you use separate shielding gas the compounds stay in your weld and contaminate it. Causing a poor weld and cracking.
.30 or .35 Welding Wire or .30 vs .35 Flux Core Wire?
Sometimes for speed these wires are casually referred to as .30 or .35 welding wires. But that's not an accurate or even the official way they are described.
It is worth noting that these sizes of welding wires are generally flux core welding wire sizes as opposed to solid welding wire.
The .0 seems insignificant but is quite important.
What is the Difference between .030 and .035 Welding Wire?
.030 and .035 are size labels and refer to the diameter of the flux core wire.
The difference? Literally .005, so there isn't much. But what difference there is, is important.
To illustrate the difference between .030 and .035 welding wire flux core and when you would choose one over the other let me tell you the story of three welders.
Joe, has never welded before but he really wants to learn. Let's see where he is at.
Joe: "Hi, I've some stuff that needs fixing up around the yard and in the past I've paid for a guy in town to weld up a few things for me."
Joe ran his hand through is wavy hair.
Joe rubbed the stubble on his chin.
"The Super Deal is flux core. I thought that would be straightforward enough for me to start with. I need some flux core welding wire and I'm not sure which to get? It can take 1 lb. or 2 lb. spools of either .030 or .035 flux core wire."
What is your flux core welder capable of Joe? What Amp range?
"Between 50 to 120 Amp, though the duty cycle talks about 105 Amp for one minute"
What will you be welding?
"All sorts I guess. The Super deal can weld from 18 gauge up to 3/16 ths and I'd like to have a bit of a go at quite a few jobs around the yard."
I'm guessing as you'll be welding all kinds of stuff. Some of it will be a bit rusty, not all lovely straight edges, maybe a bit gappy.
"Yep, that's about right. I saw some Blue Demon Flux Core at a reasonable price."
Ok, let's look at the spec sheet for that wire and compare it to what your welder can do. That'll tell us what the deal is.
The Blue Demon #2, E71TGS is .030 size, single pass flux core, this means that you're not going to be able to weld quarter inch steel, as that will need multiple passes to build up the weld.
#2 means that it is a 2 lb. spool. So that's good it'll fit in your Super Deal. You should always check what size spools your welder is capable of taking.
It's rated for use in all positions, you know flat, vertical, welding overhead.
Though I would think as a beginner you'll be mainly doing flat horizontal welds but it's good to know you should be fine for vertical welds when you build up to that.
Now to the important bit. Let's find and download the Blue Demon welding parameters chart.
Blue Demon E71TGS
50 - 175
75, 100, 150, 200
Voltage Range (Volts)
15 - 17
15 - 18
Wire Feed Range
(Inches Per Minute)
80 - 445
70 - 305
The wire parameters chart tells us what the wire is capable of and it'll have the welding parameters for all the sizes the wire is available in. The Blue Demon welding range is 50 - 175 Amp on their .030 flux core welding wire.
A nice wide range and suits your welder as it can weld from 50 Amp to 120 Amp.
Best for now, till you get more experience, to stick to the 105 Amp they talk about as the Super Deal duty cycle. Think of it as a max for now for your welding.
The voltage range on the wire is 15 to 17. You're using standard household power?
I strongly suggest you put any welder using household power on its own 20 Amp circuit as a minimum. Both the .030 and the .035 flux core wire is within the voltage range of what you have at home to power your Super Deal.
The wire feed range on the Blue Demon flux core is 80 to 445. With your little welder you're going to have to play around to find the right speed settings, as the welder's paperwork doesn't declare the wire feed speed range.
"What about the 035 wire?" asked Joe.
I was just getting to that. The welding range for the .035 is 75 Amp to 200 Amp and I note that the wire jumps quickly up from 75 to 100 Amp.
You are going to have the welder set at least half way up its Amp range to even start an arc with the 0.035 wire and you'll have a much reduced duty cycle.
"Why is that?"
The larger the wire the more power is needed to melt it.
The higher power you need, the shorter the duty cycle for your welder.
The wire feed speed range is from 70 to 305. Now we're not sure what kind of wire feed speed you're getting on your welder but this tells me that you'll want to slow the wire feed speed down compared to the .030 flux core wire.
"Which one do you think then?" said Joe.
I'd say on the spec for this wire you'd be better off with the .030. It's better suited to the welding Amp - output power of your welder and gives you the most flexibility.
Your little welder is going to have to work hard to even start to melt the .035 flux core wire and to strike an arc.
Even with flux core being more forgiving of the welder and the materials being welded. Clean off the steel, get as much rust off as you can. Get the weld edges as smooth as possible. That way your little welder won't have as much work to do.
If you can find some .030 that also supports multiple passes then you can play with welding quarter inch or 3/16 ths with the necessary preparation.
The message here is if you have an entry level welder .030 flux core wire is your friend. Your welder is unlikely to be up to welding with .035 flux core welding wire as it simply won't have the power to do much with it.
Let's talk to Andy next and Hear his Story
Andy has bought himself a Lincoln Electric 140 because he wants to experiment with using solid wire and gas. But to start he wants to weld with flux core. Which to use? .030 vs .035 flux core wire?
Let's help him make his choice;
Nice welder Andy? What is its Amp output?
"30 to 140 Amp, with a duty cycle of 90 Amp for two minutes."
What size wires does the LE 140 take?
"Both .030 or .035."
What will you be welding?
Ok, let's look at the spec sheet for that wire.
A search of the Lincoln Electric site and we have the specifications.
LE rate the NR-211-MP as capable of welding in all positions. The Lincoln flux core wire .030 and the .035 flux core wires come in 1 lb. or 10 lb. spools.
Andy can your welder take the larger 10 lb. spools?
Great, the larger spools are usually the more economical to buy. Let's take a look at Lincoln's flux core wire welding parameters chart. Great! It covers the .030 and the .035.
LE Innershield NR-211-MP
30 - 140
30, 60, 115, 130, 155
Voltage Range (Volts)
14 - 19
14 - 21
Wire Feed Range
(Inches Per Minute)
50 - 300
50 - 275
Now that's interesting, your Lincoln 140 can go from 30 Amp to 140 Amp and the Lincoln .030 flux core wire is exactly the same. LE says the .030 Innershield can weld up to half inch mild steel.
How are you going to power your Lincoln Andy?
"I've got it set up at home on its own 30 Amp circuit" Andy smiled. "I checked the manual and that's what was suggested to get the best out of it."
Great, you can see that 30 Amp is plenty just by looking at the voltage range for both the .030 and the Lincoln .035 flux core wire. What is the wire feed speed on the Lincoln 140?
Andy reached around and picked something up.
"I have the manual here, let me check it."
After a short pause and many ruffled pages.
"It's 50 to 500 inches per minute."
Perfect, the Lincoln .030 flux core wire is well suited to your welder and I guess that makes sense as it's Lincoln Electric Wire.
Now if you want to weld 5/16 ths you would need to bevel and do multiple passes with the .030 wire. And that's fine cause the Innershield MP is capable of multiple passes.
Now let's look at the Lincoln .035 flux core wire. The welding Amp range starts at 30 Amp and tops out at 155 Amp. You have your welder on a 30 Amp dedicated circuit and that's fine to weld to the max with the .035 wire.
To be honest the Lincoln .035 size of flux core wire is aimed at bigger welding machines and you can see that from its welding Amp range. Though you could certainly use it in your welder.
I think the Lincoln .030 flux core welding wire is better for you and your Lincoln 140. You'll get the most flexibility out of that wire.
The message for you here is about what you're going to spend most of your time welding.
Mostly welding thin plate then load up the Lincoln with .030.
You can get a small spool of .035 for quarter inch mild steel and above. You'll be running your Lincoln 140 on the higher settings with the .035, which is fine for short bursts.
Also remember to switch polarity when you're welding with flux core. Be sure you have the welding torch connected to the negative terminal, or welding with your flux core wire wont work.
Let's Listen to Brad's Story Next
Hi Brad, what are you up to.
"I've done a bit of welding before, I have some projects in mind that's going to need some 3/16 ths steel tubing, the welds don't need to be pretty, they need to be good, so flux core is fine, I've got myself a Hobart 190, it runs on 230 volts."
That's some machine, it should lay some nice beads for you.
"What do you think I should run in it, I'm looking at the Fabshield 21B, .030 versus .035 flux core wire?
We'll look at the wire specs, but tell me about the 190, what is its welding Amp range, voltage range and wire feed speed.
Brad scratched at the bald patch on his head.
"It's 25 to 190 Amp, up to 31 volts."
Brad picked up his phone. A few taps on the phone later he said.
"Wire feed speed 40 - 700 inches per minute."
We searched on the web for the wire specifications.
The Fabshield 21B is good for all welding positions, single or multipass. I said.
25 - 125
55, 80, 120
Voltage Range (Volts)
14 - 16
17 - 20
Wire Feed Range
(Inches Per Minute)
55 - 225
75 - 160
Looking at this Brad both wires are well within the capability of your Hobart 190. You could choose to load with either and depending on what you mostly weld, use the .035 for thicker metal and .030 for the thinner.
The only thing you have to watch out for is that you don't blow through the wire. The wires top out at 120 and 125 Amp and your welder is capable of higher than that.
"Not sure what that means."
Ok, When the current becomes too much for the wire the arc starts to destabilize. Because it takes a certain amount of Amps to melt the electrode wire.
For example going above 120 Amp would be too hot for the .035 and if it is thin metal you're welding, probably too hot for the base metal too, so bear that in mind when using .035.
It isn't going to work for all you're welding. Watch your Amp setting and wire feed speeds.
Brad is at the other end of the spectrum to Joe and Andy. He has a capable welder, in fact he needs to take care to set the wire feed speeds so he doesn’t over cook the .030 or the .035 flux core welding wires.
Choosing What Flux Core Wire to Use - 16 Points to Bear in Mind
Now you have heard the stories of Joe, Andy and Brad you should have a feel for deciding what flux core wire to use, what might be best for your situation and how to go about selecting .030 vs .035 flux core wire.
1. Your welder and what it is capable of?
How many Amps are available?
If your welder has to be set to the max to use .035 flux core wire then your welds will be problematic. You'll only be able to weld in short bursts. Because your welder is under powered for the job you're doing.
2. What size of spools will your welder take?
The smaller cheaper flux core welders are designed to be portable, typically take 1 or 2 lb. spools of wire. Look for the size of wire in the size of spool your welder will take.
3. What metal thicknesses are you welding?
Thin metals choose .030 flux core wire or thicker metals (around quarter inch and a bit above) choose .035 flux core wire.
4. Are the joints straight and clean or are they wide and variable
Wide and variable could mean you need more filler metal so .035 could be for you if your welder can melt it.
5. Flux core generally produces more spatter
6. Sometimes one size just works better with your welder!
Particularly if your welder is fully capable of taking both, experiment. Similarly one brand of flux core wire may work better regardless of the spec.
7. There is a general rule of thumb
Use .030 flux core wire for 190 Amp and under welders and .035 for welders over that and .045 for 300 Amp welders.
That said it is also about matching the wire to the metal you're welding.
8. Check whether the wire you're choosing is designed for single pass or multiple passes
Using single pass wire for multiple passes will cause your weld to be susceptible to cracking and failing. And none of us want that. Seek out the manufacturers spec for each wire.
9. Generally the larger the diameter (and the larger the spool size) the cheaper the cost
So if both are within the welding range of your MIG and cost to you is important, then go for the bigger wire.
10. If your MIG runs solid wire with shielding gas and flux core wire
Do check the polarity is correct when you're running flux core. Can't strike an arc? Check the polarity. And while you are at it check your grounding clamp has good clean contact with your piece and a good ground connection.
11. .030 and .035 welding wire In a 120 Amp machine
And allow you to get to the high end of what the machine is capable of.
However, too big a wire and the welding arc will struggle to be stable. The larger wire will take more energy to start and may quickly overheat your welder.
12. Make sure you're feeding your flux core wire through the right sized
Groove on your MIG's drive roll. Use the right sized contact tip for the size of your flux core wire.
13. Flux core is more prone to crushing
Because its center contains the shielding compounds; take care with your wire tension.
14. Watch out when you put your wire onto the spool
That the wire doesn't jump off the spool causing a bird's nest so you get poor wire feeding.
15. Keep your welding cord as straight as you can
Up to the torch head to get the best wire feed.
16. Particularly with the under 190 Amp welders
Using .035 flux core wire, you need to keep the wire feed speed down and go slow to give your welder the best chance of working with the wire.
It is best to choose the size of flux core wire based on your particular welder and what you are welding. Check the wire specifications and you shouldn't go far wrong. In the debate between .030 vs .035 flux core wire, your own situation and what welder you have will drive the choice.