This specification covers gray iron castings intended for general engineering use where tensile strength is a major consideration. Castings are classified on the basis of the tensile strength of the iron in cast test bars. This specification subordinates chemical composition to tensile strength. Castings produced to this specification are graded on the basis of minimum tensile strength obtained from special test specimens designed to standardize cooling rate. The tensile strength developed in certain casting sections may vary from test specimen values. AASHTO M 306 may be specified for drainage structure castings such as frames, grates, rings, and covers for inlets, manholes, and other structures if loading requirements exceed normal highway loading or if more restrictive dimensional tolerances are required.