These General Service 53'-6" flat cars were constructed with a welded fish-belly frame. The fish-belly frame provided an optimal distribution of tension and compression forces from the center of the car to the bolsters. In addition, fabricating a welded frame was less labor intensive than an equivalent riveted frame. The welded frame proved extremely durable holding up to really rugged service where the wood deck or the nailable wood-steel deck would need to be replace couple of times during the life of most cars. These flats commonly found it's way into maintenance-of-way service because they were still in good shape beyond the AAR interchange car-age limit. A number of builders constructed these flat cars such as the Pacific Car & Foundry (P.C. & F.), Marine Industries (Canada), Pullman-Standard, Bethelehem Steel, and including individual railroad car shops such as the Milwaukee Road and the Southern Pacific.
They were designated as FM by the AAR mechanical people. They carried anything bulky that can't be placed in box cars from tractors to finished lumber.
Wheels of Time Model Features -