MIG Welding Wire — Selection Guide

ER70S-6 handles about 90% of mild steel MIG welding in small shops and fabrication businesses. It’s the default wire for a reason: high silicon and manganese content gives good wetting, a smooth arc, and decent tolerance for mill scale. But it’s just one option in a category that covers dozens of alloy-specific formulations.

MIG wire selection comes down to three decisions: base metal compatibility, diameter, and quality. For carbon steel, the ER70S series dominates. The “70” means 70,000 PSI tensile strength, the “S” means solid wire, and the trailing number indicates the chemistry. ER70S-6 works on most structural and general fabrication. ER70S-2 adds titanium and zirconium deoxidizers for cleaner welds on critical work. ER70S-3 is the economy pick for clean material.

Diameter selection follows material thickness. Run .023 wire on sheet metal under 20 gauge with a 110V machine. Step up to .030 for 24 gauge through 3/16 inch plate, the sweet spot for most hobby and light fabrication. Use .035 for 3/16 to 1/2 inch on a 220V machine with enough amperage to keep the arc hot. Thicker .045 wire is production-shop territory requiring 300+ amp power sources.

Stainless MIG wire follows the base alloy. ER308L welds 304 stainless, ER316L welds 316, and ER309L handles dissimilar joints (stainless to carbon steel). Aluminum MIG uses ER4043 for general purpose and casting alloys, or ER5356 for higher strength on 5xxx-series and structural aluminum.

Wire quality matters more than most welders realize. Cheap offshore wire causes erratic feeding, micro-spatter, and inconsistent arc characteristics. Stick with brands that hold AWS certification and consistent copper coating thickness. Store spools in sealed bags with desiccant packs if your shop has humidity issues. Rusty wire makes porous welds.

Browse the guides below for detailed diameter-to-thickness charts, feed speed starting points, and head-to-head wire comparisons for every common base metal.