Editing 2-10-4 (section)

===South Africa===
[[File:Class 21 no. 2551 (2-10-4) a.jpg|thumb|left|[[South African Class 21 2-10-4|SAR Class 21]], ''circa'' 1937]]
In 1937, the South African Railways (SAR) placed one {{Track gauge|Cape|allk=on}} 2-10-4 [[South African Class 21 2-10-4|Class 21]] steam locomotive in service, designed for mixed traffic and suitable for light rail. It was designed by A.G. Watson, chief mechanical engineer of the SAR from 1929 to 1936, and built by the [[North British Locomotive Company]] in Glasgow. It was the only example built, and represented the maximum power obtainable on Cape gauge from a non-articulated locomotive limited to a {{convert|15|LT|t|1|abbr=on}} axle load and {{convert|60|lb/yd|kg/m|abbr=on}} rail. In order to negotiate tight curves, the third and fourth sets of coupled wheels were [[flangeless driver|flangeless]].<ref name="Holland 2">{{Holland-Vol 2|pages=73-76}}</ref><ref name="NBL">North British Locomotive Company works list, compiled by Austrian locomotive historian Bernhard Schmeiser</ref><ref name="diagram-book">South African Railways and Harbours Locomotive Diagram Book, 2'0" & 3'6" Gauge Steam Locomotives, 15 August 1941, as amended</ref><ref name="Paxton-Bourne">{{Paxton-Bourne|pages=10-11, 74-75}}</ref>

The locomotive's [[South African type FT tender|Type FT tender]] was an experimental type using six pairs of wheels in a 2-8-2 wheel arrangement, with the leading and trailing wheels as [[Bissel truck|bissel]]-type pony trucks and the remainder mounted on a rigid wheelbase. A similar [[South African type JV tender|Type JV tender]] had been built in the Salt River shops in Cape Town in 1936 as a prototype to the Type FT. The wheel arrangement was not very successful however, and not used again.<ref name="Holland 2"/><ref name="Paxton-Bourne"/>