Thus ‘Flying Scotsman’ would normally be referred to as an example of a Gresley Pacific, rather than a Gresley 4-6-2.
Small diesel and petrol engine locomotives may be described using the same system. This may be followed by D for diesel or P for petrol, and another letter describing the transmission: E for electric, H hydraulic, M mechanical. Thus 0-6-0DM denotes a six-wheel diesel locomotive with mechanical transmission. For large diesel locomotives the [[UIC classification]] is used.