Which flux core wire to choose – 0.030 vs 0.035

ine flux-cored welding wire package 0.035 thickness

One of the questions that get thrown around a lot among beginner welders and hobbyists is what size wire to use for small home repairs and projects. The sizes under debate mainly are .030 and .035 – they both are a good option, but to give you a short answer, as a hobbyist, welding between 22ga and 1/8 inch, the .030 will do the job. I think it is the most versatile size wire to use as a welder. The 0.35 would be more suitable for thicknesses from 16 gauge up to ½ inches. On the other hand, the thicker wire has more filler and flux in it, so In a lot of cases, it is much easier to find the right settings to get great quality welds even as a beginner.

If you are looking for a great flux-cored wire, I would recommend this INE one from Amazon. I have a whole post about the best flux-cored welding wires if you are interested.

What is flux core wire?

Essentially, a flux-cored wire is nothing more or less than a filler wire. What differs it from regular MIG wire is the fact that it is self-shielded. What that means is, instead of needing an extra bottle of shielding gas to carry around for welding, the wire itself has the shielding embedded. The embedded flux will create a cloud of gas over the weld buddle while welding to avoid contaminating it with air.

It has a few benefits as well, which we will discuss later on.

When and how flux-cored wire is used?

The flux-cored wire is widely used among welding enthusiasts, artists, and hobbyists. It also has it’s placed in repairs and in the construction industry. In some cases, it is also used in manufacturing, but then it is combined with shielding gas. The main reason for using it in manufacturing is the fact that it makes large scale manufacturing processes quite a bit faster.

What are the advantages of using flux-cored wire instead of regular MIG filler wire?

Using FCAW actually has a lot of positive sides depending on the context. First of all, as a hobby welder, it is way cheaper to start with flux-cored welding because the machines are cheap. The running costs are low as well because you do not need shielding gas. Depending on where you live, it can be very expensive.

Unlike with MIG, flux-cored, similarly to stick welding can be used outdoors. Regular shielding gas is usually carried away by currents of air moving outside. The burning flux, however, covers the weld even when it is windy outside.

Thanks to the missing shielding gas bottle, it is really portable as well. Small flux-only welders are light in weight. That is one of the reasons why it is used in construction and in mobile repairs.

With self-shielded wires, the polarity has to be switched for it to work. Changing the polarity helps to penetrate the weld a lot deeper. So with less powerful machines, it is possible to weld slightly thicker materials than with regular MIG welder.

Another one would be that it is capable to marry metals slightly rustier than with MIG. With MIG you can tackle plates that are covered with mill scale, but with FCAW you can also get great beads with rusty surfaces.  

Some disadvantages of using self-shielded wire

The main disadvantage would be the fact that it is messier. It produces more spatter, toxic gasses that you might inhale and after completing the bead, you have to use a slack hammer and a wire brush to clean the weld. It is really annoying in my opinion. Sometimes it is necessary even to use an angle grinder with flap discs to remove the spatter from base metals.

With flux, it is not advised to weld very thin metal like car body panels. Mainly because of the mess it leaves behind.

Which one should you choose? .030 or .035?

It is actually hard to tell which one you should pick. With many manufacturers, the quality of the wire varies a lot, so if you are a fan of a certain brand, I would do some testing to find out which works best for you. Many self-learned welders have their own ways to set up the machines, so for some thicker wire gives better results than the thinner fillers.

It also depends a lot on the machine you are using. If you have a 220v machine and you do not have to weld very thin metal then I would definitely advise you to pick up .035 size wire. If you have a small, flux-only machine, then it might be too much for your welder to handle.

There is also a joint factor to consider. If you are welding tight joints with no caps, then a smaller diameter wire is preferred. Using thick wire with tight fittings will create higher beads, which in turn will also weaken the joint.

To make it more clear, if you have a 125 amp welder or less, I would not even consider .035 wire, but with a 140 amp welder I would try, it should have enough power to run 035 flux. With machines that pack a little more punch than 140, 035 is the minimum I would go with unless you are working with very thin metals.

Tips for using FCAW method

When switching wires, also switch your contact tip to an appropriate size. For this method, since it produces a ton of spatter, I would recommend using tip one size larger than you would normally use. For example, with .030 wire use .035 contact tip. It does not make welding much more complicated, but it will save you from a lot of headaches.

With flux core, it is important that you pull the welding gun away from the puddle, not push it towards the weld to avoid contaminating the bead with flux. As a result of pushing you will get a porosity in your bead, thus the weld will be weaker.

When installing the wire, make sure that you do not tension the drive rolls too much. Since flux core is softer than regular wire, you have to make sure you do not crush it flat under too much pressure. Also, you must have a knurled drive roll.

Since flux core is way messier have some spare nozzles at hand. Also, I would recommend you to pick up some nozzle gel. I have a full article about the use of nozzle gel here. Make sure you check that out if you have never used it before.

And last but not least, be sure you are working in a well-ventilated area, or even outdoors because FCAW produces a lot more toxic gases than regular MIG welding. It will, more than likely, really damage your health in the long run. The least you can do is wear a respirator under your welding mask.


Overall I would say that flux-cored wire in a small welding machine is set up to fail, or at least it is much more difficult to get adequate beads. The thing is a lot of times the machine is not powerful enough to burn thicker wires than 0.30. The 0.35 wire has much more filler in it and it also covers the bead better with flux. So in most cases, mostly depending on your machine, the .035 would be my choice. If your machine is not capable enough, go down with size, and if you have a budget, you can always do some testing to make sure what works best for you.

My final tip would be to get yourself a small 140 amp regular MIG for home use. It is way easier and has fewer headaches with using shielding gas.