The principal freight traffic on the Festiniog railway was the carriage of finished slate from the quarries of Blaenau Festiniog to the port of Porthmadog. Specially designed slate wagons were provided for this traffic. The 3ton slate wagon was built over a period of 14 years and in all 250 were constructed. at least 93 still exsist, 79 on the Festiniog, 6 on the Talyllyn plus others in private collections. There were three different frame types with nine variations overall.