welding question for spring relocation kit

innershield/flux core vs. gas are just different methods to get the same thing: atmospheric shielding.

The limiting factor for weld penetration (and thus strength with thicker material) is amperage.

The correct amperage for any joint is based on electrode size (wire thickness) and material thickness. You can get little pocket charts for amperage guidelines at any welding supply store, or you can just google it.