Ask Phil: Will 'OO' models run on 'HO' track?


17 February 2021
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I am a British ex-pat living in the USA. I have some nice UK 'OO' locomotives and rolling stock, but I need new track. Will the 'OO' models work well on the 'HO' track that I can purchase here in the USA? Derek, via e-mail.

The short answer is yes – 'OO' models run on track with a gauge (the distance between the rails) of 16.5mm. So do the HO scale ones on sale in the US.

The reasons why 'OO' models built to 4mm:1ft and HO model at 3.5mm:1ft share a gauge are historical. UK trains have a smaller loading gauge than those abroad, and in the past, you couldn't squeeze a motor into the body if they were built to the correct scale. Making the bodies slightly larger solved the problem, but at a cost of our models being incorrect in the chassis department.

The only thing to watch is the code of the rail – this refers to the depth of the metal rails, and varies. In the UK, we normally use Code 100 track for older models, and the smaller Code 75 for more modern ones. In the US, Code 83 is also popular, somewhere between the two rail heights. This isn't a huge problem as the UK models will still run, but when joining different types of track, you might need to put a little packing under the sleepers at the join.

Wheel standards have been the same for many years, although if you have stock more than a few decades old, there might be an issue with the depth of the flanges or the distance between the backs of the wheels.

To make things easier, many UK brands export their products. Peco exports lots of track, so you might be able to buy British track from a local model store. It's such a big market for them that the OO/HO track we buy actually has HO sleeper spacing – for scale 4mm:1ft, there are too many sleepers, too close and too short. But we live with this as it keeps the cost down. Scale 4mm:1ft track is now available in the UK.

If you are concerned though, why not build a simple test track?

A single point with the length of track attached to each end, will allow you to run stock back and forth through all the checkrails and switch blades. If the model runs on this, it will be fine on the layout. As long as you don't pin the track down too hard, you can also remove it for use on the layout later.

One final point – beware American OO – this is is not the same as British 'OO', the track gauge is 19mm and your locomotives will fall between the rails. Fortunately, it's very much a niche scale, so unlikely to bother you. 

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If modelling UK prototypes in the US, it's worth joining The British Railway Modellers of North America for help and support.

If you have a model-railway question - e-mail Phil and we'll try to answer it here.

Check out more tracklaying features in our Techniques section.

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How to ballast track.

How to expand your train set.