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Introduction to Narrow Gauge


“A narrowgauge railway (or narrowgauge railroad) is a railway with a track gauge narrower than the 1,435 mm (4 ft 8 12 in) of standard gauge railways. Most existing narrow gauge railways are between 600 mm (1 ft 11 58 in) and 3 ft 6 in (1,067 mm)” – Wiki
South Africa:

At the beginning of the 20th century, 2 ft (610 mm) narrow gauge railway lines started playing a significant role in South Africa. They facilitated the transport of various agricultural and mineral produce from locations hardly accessible by road. They therefore enabled many communities to become prosperous.

These lines featured the largest and most powerful locomotives ever in existence on two foot gauge railways worldwide.

All two foot railways were operated isolated from each other. However, this did not prevent standardization and inter-changeability of rolling stock and locomotives.

Their decline started in the 1980s, the last commercial line ceased operations in the 1990s. Only a few tourist, agricultural and/or heritage railways survive.










When models of narrow gauge trains are made, there are a number of methods of describing the scale and gauge combination.

One popular scale / gauge combination is using HO scale models running on N gauge track. This effectively simulates trains running on 2’6″ gauge track.

To indicate this scale / gauge combination of such models, we usually say that they are HOn2½. The “HO” indicates HO scale, naturally enough. The ‘n’ indicates narrow gauge. “2½” means 2 and a half feet or 2 feet, 6 inches (2’6″).

However, just to confuse things, in Europe the same scale / gauge is known as HOe.

The OO equivalent in the UK is known as OO9.
This refers to OO scale running on 9mm (N) gauge track. OO9 is generally used to represent 2 foot gauge railways.

Effectively, HOn2½ , HOe, and OO9 refers to the same thing!


Narrow gauge modellers in Europe, Australia and South Africa tend to use the US method describing the scale, followed by ‘n’ and the prototype gauge in feet and inches. eg. HOn2½.

British modellers instead describe the scale followed by the model track gauge in millimetres. i.e. OO9.


Here are some of the more common names and what they mean. Using this information, you should be able to work out the meanings of any other narrow gauge scale names you may come across.

  • HOn3
    This is HO scale on track representing 3ft gauge railways. Very popular in the USA where many such lines existed. Track gauge is 10.5mm.
  • HOn3½
    HO scale on track representing 3’6″ gauge tracks as used in Australia. This uses 12mm gauge (TT) track.
  • HOm
    This is a European size.
    It is HO scale representing metre gauge railways. It uses 12mm gauge track and so is effectively the same as HOn3½.
  • HOb5¼
    Not so common, and not narrow gauge either. However, I include this to explain that some modellers run HO models on about 18mm gauge track to represent broad gauge (5’3″) trains
  • Nn3
    This scale uses 6.5mm gauge (Z) track in N scale. Known in the UK as N6.5
  • G45. Gm
    This is the same as G gauge.
    G45 is used by Peco to describe G gauge which is 45mm gauge. Gm is simply another way to describe G gauge representing metre gauge trains.
  • SM 32
    This is Sixteen Millimetre scale (16mm on the model equalling 1 foot on the prototype) running on 32mm gauge (0) track.
  • O16.5
    This is O scale on HO (16.5mm gauge) track. It is the same as On30 (O scale, “n” = narrow gauge, 30 inch prototype gauge) and On (O scale, “n” narrow gauge, 2½’ or 2’6″). 30 inches being the same as 2 foot 6 inches
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