I bought ER309L SOLID CORE STAINLESS STEEL MIG welding wire. The reel isn't marked so I have no idea what it actually is and the packaging says it's ER309L but also says it's carbon steel cored wire.
Pros
For MIG welding (GMAW) of various alloys such as mild steel and stainless steel and for direct welding of mild steel for corrosion protection; sometimes used for welding base metals "18-8" in the presence of severe corrosion conditions or dissimilar metals; ER309L stainless steel has high strength and good toughness over a wide temperature range; an inert gas is required, typically an argon/CO2 mixture.