The class K designated a class of standard Consolidations of the Southern, with over 500 built beginning in 1903. The first 128 locomotives had a boiler with 437 smoke tubes, the later ones only had 403 tubes. In addition to the Southern, the subsidiaries also received a three-digit number of the second version. From 1921, a total of 393 units were equipped with a superheater, the valve chest was also replaced and the class designation was changed to “Ks”. Depending on whether the individual locomotives had been rebuilt, they were taken out of service towards the end of the 1930s or even survived the early 1950s. 