ASTM A194 Grade 8M heavy hex nuts are manufactured from AISI 316 grade stainless steel and tested to meet ASTM A194 Grade 8M. Grade markings for A194 Grade 8M heavy hex nuts consists of the number/letter combination of 8M stamped on the nut face. Grade 8M stainless steel heavy hex nuts are intended for use in high-pressure and/or high-temperature service with ASTM A193 and A320 bolting of similar material, such as A193-B8M and B8M Class 2. Heavy hex nuts provide increased bearing surface area over finished hex nuts.