Square head bolt Standard-----GB, TB/T 2347-93, AREA or ASTM, GB and UIC Size ------ Diameter-----M20,M22,M24; 3/8″-1/8″ The length does not limit Grade-------8.8, 10.9 and also Grade 2 Grade 5 Grade 8 Surface treatment: black, electrogalvanization and Dacromet.