AASHTO M 291M

Abstract

This specification covers chemical and mechanical requirements for eight property classes of hex and hex-flange carbon and alloy steel nuts for general structural and mechanical uses on bolts, studs, and other externally threaded parts. <br>NOTE 1-Throughout this specification, the term class means property class. <br>NOTE 2-Requirements for the four classes 5, 9, 10, and 12 are essentially identical with requirements given for these classes in ISO 898/11. Requirements for Classes 8S and 1OS are essentially identical with requirements in an ISO 4775 Hexagon Nuts for High-Strength Structural Bolting with Large Width Across Flats, Product Grade B, Property Classes 8 and 10. Classes 8S3 and IOS3 are not recognized in ISO standards. <br>Classes 8S3 and lOS3 nuts have atmospheric corrosion resistance and weathering characteristics comparable to those of the steels covered in Specification A 588/ A 588M. 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. <br>The nut size range for which each class is applicable is given in the table on mechanical requirements. <br>Appendix X1 gives guidance to assist designers and purchasers in the selection of a suitable class. <br>Appendix X2 gives data on the properties of slotted hex nuts and hex jam nuts. <br>NOTE 3-This specification is the metric companion of Specification A563. <br>Terms used in this specification are defined in Terminology F 1789 unless otherwise defined herein. <br><strong>* A Summary of Changes section appears at the end of this standard.</strong>