To wit, quoting the 1974 "Car & Locomotive Cyclopedia": "Truck: The general term covering the assembly of parts comprising the structures which support a car body AT EACH END [emphasis mine], (or, in the case of articulated cars, the joint support of two abutting car ends) and also provide for attachment of wheels and axles." "Truck frame: A structure made of cast steel in one piece, to which the journal boxes or pedestals, springs and other parts are attached, and which forms the skeleton of a truck. See Truck Side Frame." "Truck Side Frame: The longitudinal portion of a truck structure, on the outside of the wheels, which extends from one axle to the other, and to which the journal boxes and bolsters or transoms at attatched or form a part." And industry references and advertisements generally call out the number of wheels a truck has, not its number of axles, if they bother calling it out at all. Scott Chatfield
S.A. McCall