How To Choose Between 030 and .035 Flux Core Wire?

How to select Welding Amperage? x
How to select Welding Amperage?

Wire thickness is important and can affect overall weld quality. Mechanical properties like tensile strength and elongation can be dictated by wire diameter. I am asked quite often about the differences between .035 and .030 wire, as well as if there is a definitive answer as to which size is better.

The answer is not always straightforward, as it depends on the specific project at hand. In this post, you will learn everything you need to know about choosing between .030 and .035 flux core wire size.

How To Choose Between 030 and .035 Flux Core Wire?

What is flux core wire?

Flux core wire is a self-shielding welding wire that uses an external flux to create a shielding gas around the arc. The flux core wire produces a high-quality weld without the need for an external shielding gas like carbon dioxide (CO2) or argon.

The flux in the wire is designed to protect the molten metal from exposure to oxygen and nitrogen, which will create porosity and inclusions in the weld.

This way, welding with such wire is more economical, less time-consuming, and more environmentally friendly compared to using a more expensive CO2 or argon mix.

Where is the flux-cored wire used?

The main application for flux-cored wire is in construction, farm repairs, automotive manufacturing, and structural steel erection. It’s also used in pipelines and general fabrication.

Why should you use Flux core wire instead of MIG filler wire?

MIG welding is a process that uses gas to protect the weld from atmospheric contamination. The process is more expensive than flux-cored wire and time-consuming too. In addition, flux-cored welding can be done outdoor, even in a strong wind, while MIG welding cannot.

TIP: If your metals are slightly rusted, you will have more chance of creating a better weld with flux core wire than MIG.

What are some disadvantages of using Flux Core Wire instead of MIG filler Wire?

When welding with Flux Core Wire, there will be a lot of spatter present. In addition, flux-cored wire produces more fumes and toxic gasses than MIG welding.

When you analyze weld look, Flux-cored is just not as pretty as MIG welds. In most cases, you will need to help yourself with an angle grinder to remove all the spatter made during the welding process.

Difference between. 030 and .035 flux core wire size

030 and .035 flux core wires are two common thicknesses and this post is all about explaining them more in detail. We will start with the most important differences.

Amount of amps needed

To maintain a consistent and proper welding arc, the wire thickness has to be proportional to the amount of electricity.

Thick .035 wire needs higher amps than .030 wire in order to maintain the same arc. So, if you’re using a machine with lower amps, you’ll need to go for the .030 wire size.

Porosity and Inclusions

The .035 flux core wire generally produces less porosity and inclusions so If you’re welding on rusty metal, it will be more suitable from the start.

Ease of Use

The .030 Flux core wire is easier to use when welding on thinner metals or when you are still learning how to weld. It is mainly because .035 thickness requires higher amperage.

Deposition rate

The deposition rate is how fast the weld puddle is deposited. A higher deposition rate means more weld metal is deposited in a given time period.

In practice, it will mean that when you use .030 wire, you will need to work slower than using .035 to achieve the same weld deposition.

Tensile strength and Elongation

Tensile strength is the maximum amount of stress a material can withstand before breaking. On the other hand, Elongation is the measure of how much a material will stretch before breaking.

The .030 wire has a lower tensile strength and elongation than .035 so may not be able to handle as much stress, leading to a weaker weld.


The price of flux core wire can vary depending on the manufacturer and the quantity you purchase. However, in general, 030 wire is cheaper than .035.

Which Flux Core Wire should you choose?

Your choice will largely depend on the type of welding you will be doing.

Amps available in your welder

The higher the amps available in your welder, the thicker the wire you can use. If you need to set your welder to max power when using 035. Flux Core wire, it will take you more time to finish your project. In addition, you will need to weld in Short bursts.

TIP: If you haven't bought a welding machine yet, search for one capable of higher amps.

Material being welded

Metals that have a thinner material thickness of around 1/8 inches or less are good for .030 wire. Anything above and up to 1/2 inches you might want to go with the .035. because it will have better penetration and less chance of warping the metal.

NOTE: Experienced welders have a high chance of success with 035. Flux Core wire is even with slightly thicker metals but a learning curve is needed.

Your skill level

As a beginner welder, you might find it easier to use 030. flux core wire because the lower amperage is less likely to cause problems.

Size of wires in your spool

The last thing you need to consider is the size of the wire in your spool. If you’re using .030, the flux core wire will be coiled around a smaller spool than if you’re using .035.

NOTE: If you are using a welder with a smaller wire feed capacity, you might have trouble feeding the thicker 035 wire through the machine. In this case, you will have to choose 030 flux core wire instead.

Related Questions

What is the difference between flux core wire and solid wire?

Flux core wire has a coating of flux inside the wire that helps to create a better weld. This wire is designed for use with gasless welding machines. Solid wire does not have flux inside and must be used with a welding machine that provides an external gas shield or gasless.

Which flux core wire should I use for welding aluminum?

Flux core wire is not recommended for welding aluminum because it creates a brittle weld that is susceptible to cracking. You should use a solid wire designed specifically for welding aluminum.

Can I use a MIG gas shield with flux core wire?

Yes, you can. Flux-cored welding involves an external flux. But you can use a MIG gas shield with flux-cored wire too.

Read Next