Based on cars used in the U.S. and Canada since their construction between 1964 and 1966, prototypes for the Rapido Trains HO Scale ACF PD3500 Flexi Flo Covered Hopper was an early innovation in pressure-differential commodity unloading. New York Central was the largest customer for these unique cars with a fleet of 220 ordered in several groups and another seven were ordered by Shippers Car Line SHPX. The cars operated in various PC and CR patched schemes until they were transferred to Conrail's Merchants Despatch subsidiary and many were sold with the cars moving on to service throughour the continent. These models replicate several prototype variations of the prototypes. Other features of this ACF PD3500 Flexi Flo Covered Hopper model include full underbody detail including discharge piping, coupler cut levers and other details, metal Macdonald-Cartier magnetic knuckle couplers.