The practice started in 1948 included letter indicating the vehicle type and model series; letters L, and gradually replaced by B, were used with bus chassis, although sometimes these applications were fitted with lorry cabins and superstructures. L-model buses can be distinguished by two-digit model series codes; later L made a return to Sisu model names in lorries, but with three-digit model numbers. Since 1970 the engine configuration of bus chassis was indicated with a second letter: BE meant front engined, BK middle engined and BT rear engined chassis. Conventional cabin lorries were K, U, UM, UP, L, LP, LM, LV and R. Lorries with forward control cabin were KB, M, MS, A, AH, AS, MA, MI and MK. Terminal tractor and mobile crane chassis models started with letter T. The model code was followed by an engine type code, consisting two or three letters.