TOPS numbers are on the front of the cabs under the driver's window in a non-standard typeface (Plantin, the then corporate typeface of Royal Mail), and the units were numbered 325001 - 325016. The units are fitted with large round oleo buffers, and have no gangways between carriages. They carry a livery of Royal Mail red, with two yellow stripes running along the lower bodyside before turning sharply backwards and pointing up towards the roof, black cab window surrounds and a full yellow warning panel. Each set is made up of four cars, with roller doors in place of sliding ones and no windows. Each car has two roller shutter sliding doors on each side and is designed to hold up to 12 tonnes. They have a pantograph to pick up power from the 25 kV AC overhead lines, and also a shoe to pick up power off the 750 V DC third rail. They cannot work in multiple with any other multiple unit stock, but are fitted with drop-head buck-eye coupling and can therefore be hauled by locomotives. The units were built in such a way that they could easily be converted for passenger use if no longer required for mail services.