The RF class was built on the same underframe and with the same dimensions as the XL box car. About 2,800 were built beginning in 1906 for PRR and PL with a number of billboards. The XM class was also produced, identical to RF in appearance but without ice bunkers. A number of cars were transferred to express service under contract to Adams Express and later, American Railway Express. The cars ran for FGE as late as 1934.
Original kits cover the cars without safety appliances and with wood roofs and wood end ladders.
General decal lettering covers all one-color billboards used on the cars thoroughout their lives.