This specification2 covers chemical and mechanical requirements for eight grades of carbon and alloy steel nuts for general structural and mechanical uses on bolts@ studs@ and other externally threaded parts. NOTE 1??See Appendix X1 for guidance on suitable application of nut grades. The requirements for any grade of nut may@ at the supplier's option@ and with notice to the purchaser@ be fulfilled by furnishing nuts of one of the stronger grades specified herein unless such substitution is barred in the inquiry and purchase order. Grades C3 and DH3 nuts have atmospheric corrosion resistance and weathering characteristics comparable to that of the steels covered in Specifications A 242/A 242M@ A 588/ A 588M@ and A 709/A 709M. The atmospheric corrosion resistance of these steels is substantially better than that of carbon steel with or without copper addition (see 5.2). When properly exposed to the atmosphere@ these steels can be used bare (uncoated) for many applications. NOTE 2??A complete metric companion to Specification A 563 has been developed??A 563M; therefore@ no metric equivalents are presented in this specification. Terms used in this specification are defined in Terminology F 1789 unless otherwise defined herein. 2 For ASME Boiler and Pressure Vessel Code applications see related Specification SA ?C 563 in Section II of that Code.