Is there a way to visually distinguish the difference between a Class 1 and Class 2 stainless steel bolt?
Yes there is. A193 and A320 grades B8 and B8M are assumed to be Class 1 unless otherwise specified. Class 1 fasteners are carbide solution treated, while class 2 fasteners are carbide solution treated and strain hardened. The work hardening that occurs in the manufacturing of Class 2 fasteners increases their strength. Class 2 fasteners are differentiated by the letters “SH” after the steel grade and an underline for A193 steels, and the steel grade with an underline for A320 steels. The marking typically appears on the heads of bolts or the ends of threaded rods. For both A193 and A320, the marking requirement historically was only the underline, the “SH” lettering was added in approximately 2006.
|A193 Grade B8||Type 304||High temperature / High pressure||B8||B8SH|
|A320 Grade B8||Type 304||Low temperature||B8||B8|
|A193 Grade B8M||Type 316||High temperature / High pressure||B8M||B8MSH|
|A320 Grade B8M||Type 316||Low temperature||B8M||B8M|