unlikely to move) took numbers in the 0xxxxx series. For more details see below. The same series was used for Mark 2 coaches built in the 1960s, but when Mark 3 carriage was introduced in the early 1970s new number ranges were carved out of the old series. These new ranges were perpetuated for Mark 4 carriages in the 1980s, and were as follows: Diesel multiple unit builds in the 1980s utilised the 52xxx, 55xxx, 57xxx and 58xxx series for carriages, all of which were motored. The 55xxx and 58xxx contained a mix of driving and non-driving motors, but the 52xxx and 57xxx cars were all driving motors. Some series have been used for conversions of carriages, e.g. 63xx has been used for a variety of miscellaneous carriages, including generator vans and observation saloons. A major change came in May 1983 when prefix and suffix letters was abandoned, and any carriage that had the same number as another carriage or a locomotive was renumbered. The programme worked as follows: Further renumberings have taken place as new locomotives were introduced. Most have involved only a handful of carriages, but a major one saw carriages in the 920xx series renumbered 929xx when Class 92 locomotives were introduced. This series has been perpetuated, though the series have been adapted for new generation multiple unit stock. For instance, the latest diesel multiple units have reused the 50xxx and 79xxx series for driving motors and the 56xxx series for non-driving motors. In the electric multiple unit series, Class 390 Pendolinos have reused the 68xxx and 69xxx series. When BR began to build air braked wagons they had B prefixes, but this was dropped and six-figure numbers were used without prefix. Prefixes were added, however, if and when carriages and wagons transferred to the departmental/engineers' fleets. Privately owned wagons and carriages were allocated numbers with an integral prefix to differentiate them from the BR number series, with carriages taking numbers in the 954xx and 99xxx series. From 1986, those carriages in the 99xxx series which otherwise duplicated BR bullion and exhibition van numbers were renumbered, and from then on the prefix was not essential for identification. Post-privatisation, with all carriages being privately owned, this list was discontinued and many carriages reverted to carrying their original BR number. Departmental and Internal User Stock Most departmental and internal user vehicles are converted from revenue-earning stock; only a small