Tuesday, April 12, 2011


Photo by Steve Jones
Several weeks ago I used a few of my postings to try and explain the differences between some of the various model railway gauges that are available.
I covered OO, N and O gauges and had intended to continue with HO but have, so far, failed to do this. Well, this oversight, despite my title, is clearly no laughing matter so I am turning my attention to HO gauge now and will cover some of the other, less popular gauges, in future postings.
HO is by far the most widely used modelling scale in the world and is dominant in North and South America and all of Europe, with the exception of the UK where OO prevails. It has a nominal ratio of 1:87, with models being built to a scale of 3.5 mm to 1 foot and running on track that is 16.5 mm gauge. This is very similar to the British OO gauge of 1:76 or 4 mm to the foot and which uses the same gauge of track.
However, the scale:gauge ratio of HO is almost perfect for standard gauge prototypes whereas, for OO, 16.5 mm gauge track is really too narrow.
HO was introduced in 1935 by Marklin as a smaller alternative for those people who could not afford to model in O gauge. Now, we must remember,  that O gauge is more properly known as 'nought' or 'zero', rather than the letter O. The name HO derives from the term 'Half O' although it was not really until after the war that manufacturers made a decent attempt at producing accurate models to a consistent scale.
Nowadays there is a vast range of ready-to-run models available although in Europe, surprisingly, there are few suppliers of locomotive and rolling stock kits. However, the situation is different in America with a wide variety of kits for rolling stock and detailing parts. When it comes to scenic materials, structures and accessories, etc, the range is similarly huge and some of these are suitable for use on an OO gauge layout.
In terms of space requirements, HO models can be considered much the same as OO and HO models are large enough to feature fine detail and are sufficiently robust yet small enough to allow a reasonable railway to be built in a sensible space.
In Europe, almost all aspects of the standards for this and other scales are governed by NEM regulations, with NEM being an abbreviation of the German phrase meaning 'European Model Railway Standards'. These recommendations are only advisory and the technical tolerances are, in some cases, quite wide, however, most manufacturers do try and adhere to these standards.

Finally, I wanted to show you, graphically, the difference in size between HO and OO  but have no HO models that I can photograph. However, I did find the terrific picture, by Steve Jones, on the Internet showing two Class 66's in 3.5 mm (above) and 4 mm (below) which I think does the job quite admirably.

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