What's Better, T409 or T304 Stainless Steel Exhaust Components? The most frequently used stainless steel in performance exhaust system is T409. Found in Magnaflow exhaust and many stainless mufflers, this mixture has enough chromium and nickel to resist corrosion. But, it lacks the strength to be used for fasteners. Next up in the ring for corrosion resistance and all-around toughness is the T304 steel used in Borla exhaust and Cobb exhaust. This is the highest quality stainless steel used in the automotive world. It is most often found in exhaust tips. Super tough and nearly impervious to rusting, T304 has around 20% chromium and 10% nickel content in the alloy. In fact, the ferrous metal content is so low that magnets won't stick to it, making identifying T409 from T304 very easy.
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