Anyone care to explain what the big differences are between 304 and 409? I know one is stainless probably 409. and one is mild steel 304... I know mild steel gets water spots and stuff but what i'm worried about is the longevity between the two. The reason I ask is because i'm going to be buying an exhaust soon so I wanted to know... Thx

 

No, they are both stainless steels. 304 is an austinetic (the structure) stainless which means it has nickel in place of iron. It is not as hard as 400 series stainless steels which are martensetic in structure and contain a much higher iron content. Remember it's stain less steel not stain proof steel. 304 is more corrosion resistent than 400 series but it's also softer..........which may not matter in your exhaust system. 304 will outlast the 400 series in corrosive service.