Solid MIG welding wire is a single, solid strand of metal, while flux-cored MIG welding wire is a hollow tube filled with flux. Flux-cored wire produces more smoke and spatter, but it can be used for thicker materials and out-of-position welding.

The type of shielding gas you use will depend on the type of metal you are welding. For most steels, a mixture of argon and carbon dioxide is used. For aluminum, pure argon is used. For stainless steel, a mixture of argon and helium is used.

The size of MIG welding wire you use will depend on the thickness of the metal you are welding. For thin metal, a wire diameter of 0.023 inches or 0.030 inches is used. For thicker metal, a wire diameter of 0.035 inches or 0.045 inches is used.

When choosing MIG welding wire, you need to consider the type of metal you are welding, the thickness of the metal, and the type of shielding gas you are using. You should also consider the specific requirements of your project.