ASTM A182 GRADE F5 vs F5a ASTM A182 GRADE F5 vs F5a sgpmi14 (Industrial) (OP) 24 Apr 17 15:00 I would like to know what the main difference is and why would you choose one over the other? What applications they differ in as well as in what way F5a is superior? Your help is greatly appreciated! RE: ASTM A182 GRADE F5 vs F5a metengr (Materials) 24 Apr 17 20:51 The main difference can be found in the ASTM specification, if you have a copy. Hint: strength. The same hint applies as to why I would select F5 over 5A.