 The code books are assigned specific letters and numbers for easy reference, and many welders will refer to a specific code letter/number combination when referring to the code book.Different welding methodologies, inspection methods, and metals are published under different codes.For example, AWS B1.11 explains how to visually examine welds; AWS B2.1-1-004 explains welding carbon steel of thickness range of 18 through 10 gauge with semiautomatic metal gas arc welding; and AWS C2.20/C2.20M explains metalized zinc cathodic protection systems.