Railroads bill for their services based on the weight of the commodity shipped. This means they and their customers must have accurate scales to determine the weight of loaded and empty cars. Periodic inspections are done using a scale test car. Measuring just 13' long, these tiny cars have a verified weight anywhere from 20 to 50 tons to activate the scales. Because of their small size, they are moved at slow speed and coupled at the rear of the train.
 
A must for steam or diesel-era layouts, these plastic cars feature easy construction and include a weight so they can be moved in trains like the prototypes.