When it comes to stainless steel fasteners, the designations A2 and A4 appear everywhere, yet they are not always clear to those who use them daily. Both refer to austenitic stainless steels, but with significant differences in terms of corrosion resistance.
A2 offers good resistance in moderately corrosive environments and is often the standard choice for general applications. A4 contains molybdenum, which enhances its resistance in more aggressive environments, such as marine settings or where certain chemicals are present.
For designers and installers, the practical rule is simple: choose A2 for ‘normal’ environments and A4 when the risk of corrosion is higher or maintenance is difficult. Carefully assessing the service environment helps prevent premature replacements and unexpected costs.