ASTM A194 Grade 2HM heavy hex nuts are quenched and tempered alloy steel nuts and are 100% hardness tested. ASTM A194 covers carbon steel, alloy steel, and stainless steel nuts for bolts in high pressure or high temperature service. Grade markings consists of both the grade symbol "2HM" and the manufacturer's identification mark. They are usually paired with A193 Grade B7M fasteners in applications where hydrogen sulfide gas exposure may lead to hydrogen embrittlement problems. Dimensional specifications are governed by ASME B18.2.2. Heavy hex nuts provide increased bearing surface area over finished nuts such as J995 Grade 5 nuts.