1.1 This specification covers seven classes of carbon steel tires for railway and rapid transit use.

1.1.1 Class AFor untreated driving tires for locomotives in passenger service.

1.1.2 Class AHTFor heat-treated driving tires for locomotives in passenger service.

1.1.3 Class BFor untreated driving tires for freight locomotives and tires for locomotive-truck, tender-truck, trailer and car wheels, and miscellaneous service.

1.1.4 Class BHTFor heat-treated driving tires for freight locomotives and tires for trailer wheels.

1.1.5 Class CFor untreated tires for switching locomotives.

1.1.6 Class CHTFor heat-treated driving tires and switching locomotives and tires for locomotive-trucks, tender-trucks, trailer and car wheels, and miscellaneous service.

1.1.7 Class DHTFor heat-treated driving tires for locomotives with light braking conditions, heavily loaded trailer tires, and rapid transit wheels where off-tread brakes are employed.

1.2 Supplementary requirements, including those in the general requirements of Specification A 788, are provided for use when additional testing or inspection is desired. These shall apply only when specified individually by the purchaser in the order.

1.3 The values stated in either inch-pound or SI (metric) units are to be regarded separately as standards. Within the text and tables the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.

1.4 Unless the order specifies the applicable "M" specification designation, the tires shall be furnished to the inch-pound units.