||Collett's standard 0-6-0PT's with 4' 7½" wheels. The 863 engines of this type, constructed between 1929 and 1949, constitute the largest class in the country. There are a few detailed variations, but all are in the main of one uniform design. The principal deviations from the standard are found in engines 9700-9711, which are fitted with condensing apparatus for working through the Metropolitan line tunnels in the London area. The design of the cab also underwent a change with the later-built ones. Nos. 6700-6779 were fitted with steam brakes only and confined to shunting duties, mainly in the South Wales division. The other engines, although their principal function is shunting and short-haul freight trains, are vacuum fitted and are frequently to be found working passenger trains. The order of construction of the various batches was: 5700-5799, 6700-6749, 7700-7799, 9700 (first numbered 8700) 8701-8799, 8700, 9701-9799, 3700-3799, 3600-3699, 4600-4699, 9600-9661, 6750-6759, 9662-9682, 6760-6779. Withdrawal of the older engines commenced in 1956, the first constructed, No. 5700, and No. 5762 being taken out of service in that year.