Over a period from 1896 to 1916, the NSWGR received a total of 280 Consolidations of the class T.524, designated D50 from 1924. They were described as a successful combination of the features of American and British locomotive design. Most were built by British companies, except for 30 by Clyde Engineering.

Ten which were under construction at North British during the First World War were initially used by Great Britain in the war. Since the NSWGR refused to accept the worn-out machines after the war, they ultimately ended up with Nord-Belge. The Commonwealth Railways used eight identically locomotives as class K.

They had a typically British-looking boiler with a Belpaire firebox. To make it easier to run through curves, the wheels on the second and third driving axles had no wheel flanges. The last 75 locomotives were built directly with a superheater and showed such good results that many of the existing ones were also retrofitted.

They were now the NSWGR's ultimate standard freight locomotive. Despite their age, it took a long time for their number to decrease significantly. In 1954 there were still 220 in use and in 1964 there were still 113, but increasingly in shunting service. Some even got automatic couplers for this task from 1960 onwards. They disappeared from active service in the 1970s and four remain today, none of which are operational.