What is EM gauge?

16 May 2019
for-upload-17947.jpg Black Country Blues Layout
This increasingly popular track gauge has its pros and cons, here's an explanation of what it is.

EM gauge short for Eighteen Millimetre gauge is a track gauge (or distance between the rails) popular with British railway modellers. Its origins can be traced to the overscale British locomotive bodies used on OO gauge track. The British loading gauge is smaller than that of continental European countries and many others around the world. This created a problem for British manufacturers of early OO gauge models because the bulkier and more primitive motors struggled to fit inside smaller British bodyshells. Had these motors fitted, the main modelling gauge in Britain would have been HO, or 1:87 scale, half the size of O gauge, from which its name originates (Half O). Seeking to keep the track gauge the same as HO for compatibility with other countries, manufacturers chose to make the bodyshell larger and overscale to accommodate the running mechanism.

The compromise between track gauge and bodyshell size of OO gauge has remained in place to-date, despite the miniaturisation of motors and mechanisms. Attempts to introduce HO scale to Britain have been numerous, by manufacturers and associations alike, though sales have never matched those of OO gauge which has become the standard British railway modelling scale.

In search of a better compromise between the track gauge and the overscale bodyshell, modellers in the mid-1950s created EM gauge, using an 18mm track gauge. Today, this has evolved into 18.2mm gauge, but retains the name EM gauge and is supported by the EM Gauge Society whose aim is to promote the track gauge. Presently, no large RTR manufacturer has released a model to EM gauge wheelset standards, though some facilitate the replacement of wheelsets on rolling stock by making the brake blocks wider to accommodate the wider wheels.

The benefits of EM gauge are solely visual - the track appears closer to scale and more refined, however, conversion of rolling stock and locomotives puts many off. The EM Gauge Society helps modellers who want to upgrade to the gauge with conversion kits and advice, whilst producing a magazine for its membership to support and share projects.    

(Right) The RMweb project layout 'Black Country Blues' employs EM gauge track for a finer, more scale appearance.

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Liverpool Lime Street

'Liverpool Lime Street', a 30-year labour of love for John Holden and his team of talented modellers. The hand-laid EM gauge track is prominent in this photograph.

Want to see more EM gauge layouts? Visit the other scales category in our layouts database.