A spool of wire is the cheapest part of a MIG setup — and the one that decides whether your welds run smoothly or fight you all day. Get the diameter and type right for the metal and thickness, and most feed problems disappear. Here's how we'd choose at the counter.
Wire diameter — match it to the metal thickness
Diameter sets how much current the wire carries and how thick a section you can weld. For the hobby and general-fabrication kit we sell most of, three sizes cover almost everything:
- 0.6mm — thin sheet and car bodywork (roughly 0.8–3mm). Lowest heat, kindest on thin steel, least likely to blow through.
- 0.8mm — the do-everything diameter for general steel from about 1mm up to 6mm. If you only buy one spool, this is usually it.
- 1.0mm — heavier steel (6mm+) and faster fill on production work, where your machine and gas can support the extra current.
Too big a wire on thin steel runs cold and dumps a tall, ropey bead; too small on thick steel burns back and struggles to fill. When in doubt, drop a size — a thinner wire is more forgiving.
Set the liner, tip and rollers to suit
The wire diameter has to match the rest of the feed path or you'll get birdnesting, erratic arc or burn-backs. Change the wire size and you should check three things: the contact tip (stamped with the wire size — 0.8 wire needs an 0.8 tip), the drive rollers (grooved to size, and the right groove uppermost), and the liner (a steel liner for steel wire; a plastic/PTFE liner for soft aluminium). We keep tips, liners and rollers on the shelf for the common machines.
Solid wire vs gasless (flux-cored)
Solid wire needs a shielding-gas bottle but gives a cleaner weld with little spatter and no slag to chip off — the choice for indoor work and anything that needs to look tidy. Gasless (flux-cored) wire carries its own shielding inside the wire, so there's no bottle to buy and it copes with wind that would ruin a gas-shielded weld outdoors. The trade-offs: more spatter, a slag layer to clean, and you must switch the machine to reverse polarity (earth to positive) for gasless. Check your manual.
Quick steer: Indoors and want it neat? Solid wire + gas. Outdoors, on site, or no bottle? Gasless wire — and don't forget to flip the polarity. Welding stainless or aluminium? You'll need a matching specialist wire, not steel wire.
Stainless and aluminium need their own wire
You can't weld stainless or aluminium with mild-steel wire. Stainless uses a matching grade (308LSi is the usual all-rounder) under pure argon or an argon mix. Aluminium uses a soft alloy wire (4043 or 5356) that needs a PTFE liner and ideally a spool gun or push-pull torch, because the soft wire kinks easily through a long steel liner. Tell us the alloy and we'll match the wire and the gas — there's more on gas choice in our shielding-gas guide.
Keep wire dry and feeding cleanly
Wire is steel — it rusts. Rusty or contaminated wire feeds badly and contaminates the weld. Store spools in a dry place, and if a part-used spool has sat for months, run a foot off before trusting it. Keep the gun liner clean and renew worn contact tips; most "the machine's playing up" calls we get are really a worn tip or a tired liner.