BR Class 4 Locomotive

The class was designed at the ex-LNER works at Doncaster which was also responsible for building 25 of the 115-strong class. The remaining 90 were split between Horwich and Derby Works.
The last in the series, No.76114, was also the final steam engine to be constructed at the 'Plant' (as Doncaster works was known). The Standard Four Mogul was essentially a standardised version of the LMS Ivatt Class 4, and was primarily intended for freight use.
Although a BR Standard the class did not have the same design of wheels as the Swindon-built 82XXX and 77XXX Class 3 engines which also had 5-foot-3-inch (1.600 m) driving wheels, yet all three locomotive classes share the same cylinder casting.
The cylinder covers of engines built early in the programme of construction were fitted with "screw-in" type pressure relief valves. From September 1955 revised cylinder covers were introduced for renewals incorporating "bolt-on" type pressure relief valves.^[1]

With its 5-foot-3-inch (1.600 m) diameter driving wheels this sixth of the BR standard designs was clearly biased towards freight working. An axle-loading of only 16 tons 15 cwt meant its route availability was virtually unrestricted. Batches were allocated to every BR region except the Western.

The above from Wikepedia

Many thanks to Bluebellnutter at en.wikipedia for the above picture of a class 4