In the UIC classification, the Co-Bo or Co′Bo′ wheel arrangement features two uncoupled bogies. The "Co" bogie has three driven axles and the "Bo" bogie has two.
The British Rail Class 28 is the first (and only) UK locomotive with a Co-Bo wheel arrangement. Other examples worldwide include the class DE10 and DE11 diesel-hydraulic locomotives in Japan.
Some Engerth steam locomotives were built to the Fink system, with the four trailing wheels driven by a crankshaft and connecting rods, thus making them 0-6-4-0Ts instead of 0-6-4Ts.
BoCo is a fictional Co-Bo locomotive, a British Rail Class 28. The locomotive appeared in the Thomas the Tank Engine book Main Line Engines.[1]