You may notice two types of stainless steel used in making polished nerf bars: T304 and T403 steel. Both are highly corrosion-resistant alloys. T-304 has the highest chromium and nickel content of any stainless steel, making it the most corrosion-resistant material in the industry and the most commonly used stainless steel. T403 stainless steel is highly corrosion-resistant, though it is a different alloy developed for high impact strength. Nerf bars made from either of these materials are highly corrosion resistant, will likely not rust for the life of your vehicle, and have the strength last through many thousands of uses.