The most numerous class of steam locomotives on the South Australian Railways was the 2-6-0 class Y built between 1885 and 1898 for their Cape gauge network. Noticeable features were the low running boards which were sloped upwards at the front to provide space for the inclined cylinders and a dome that had the same height as the chimney. They were intended for freight service, but sometimes also used for passenger trains.

50 were built by Beyer, Peacock & Co. in England, 77 by James Martin & Co. in Australia and two more by the Railway's own Islington workshops. More locomotives of nearly identical design were built as Silverton Tramway class Y, Tasmanian Government Railways class C and Western Australian Government Railways class G. Between 1904 and 1924, 58 were rebuilt to class Yx. These got a new boiler with Belpaire firebox and a pressure of 185 instead of 150 psi. 

Later some where used on the timber lines of Western Australia, while others were sold to railway construction companies. In 1941 and 1942, 18 were sold to the Commonwealth Railways to become class Nfb. In 1948, seven of these were sold again to the Tasmanian Government Railways and became class F. Today ten are preserved, with Yx141 being operational.