ER308 is a welding consumable tailored for welding 304 stainless steel, while ER304 is simply another type of 304 stainless steel. To use an analogy: it’s like using ordinary fabric to patch a piece of high-end clothing. While the colors may appear similar, a professional tailor will use specially matched wire and fabric to ensure the patch’s strength, color durability, and overall aesthetic. Substituting ordinary fabric may not be noticeable in the short term, but after a few washes, color differences, shrinkage, or cracking may occur.