Chord Article 1.


What is Gauge '0'.
by Ian Major.

What a strange question to ask. Everyone knows what Gauge '0' is! Or do they? Well, following some confusion last year which resulted in a Midland 6 Wheel carriage getting stuck in a tunnel on our club '0' Gauge layout, I decided some clarification was needed. The problem is that Gauge '0' covers more than one scale, and even some variation in gauge. It is safe to say that '0' evolved and was not designed. Like all evolutionary beasts, it comes in various guises.

Railway modelling has to define both scale and gauge. In theory, if you specify the scale, the gauge automatically follows eg in 7mm/ft scale standard gauge is 32.96mm. However, for practical reasons, the gauge of model railways has not always been to exact scale. So when you refer to British '0' you are defining a track gauge and a scale. American '0' has the same gauge, but a different scale.

The source of the mess.

Models of railway vehicles, have been around as long as their full size counterparts. Originally, they were built for demonstration purposes, or to give apprentices practical experience. These were the forerunners of today's Model Engineers.

It the mid 19th Century, toy railways made an appearance. The first was believed to have been made for the young Prince Imperial of France about 1860. The early toys were used on the floor without track, so gauge was not an issue, and scale was arbitrary.

Towards the end of the century, with the development of self propelling locomotives (steam or clockwork), came track. This signalled a miniature version of the 'Gauge Wars'. Each manufacturer tended to do their own thing. Marklin, however, were pioneers in standardisation, with their gauge numbers 0 to 3, which ranged from 35mm to 75mm.

Companies in America such as Ives and Lionel settled on 1¼ inches for Gauge '0' (32mm). Since this was the largest market, the European companies fell into line. At this time, though, the 'standard' model gauge for Lionel was 2.125 inch gauge.

Although the gauge had become fixed, the scale was still variable.

Enter Henry Greenly.

Henry Greenly was one of Britain's early Model Engineers. His works include the design of locomotives for the Romney Hythe and Dymchurch Railway. He was also consultant engineer to Bassett- Lowke. This British company started by importing models made by German companies such as Bing. The First World War resulted in these supplies being cut off, so Bassett-Lowke moved into manufacturing their own products. They produced both toy railways on pressed track and serious models requiring two track/wheel standards. In his consultant role, Greenly specified these standards, calling them ordinary and special. These determined the scale as 1:45 to be used with a gauge of 32mm.

In the USA, the Great Depression of the 1930's saw the demise of companies that only produced the larger scale models. Those that produced Gauge '0' survived. In 1935, the National Model Railroad Association of the USA (NMRA) was formed. It produced its own, entirely imperial, standards. Included amongst these, '0' was based on a gauge of 1¼ inch and a scale of ¼inch/ft, a scale ratio of 1:48.

Coincidentally smaller gauge/scales were appearing notably '00/H0'. In 1941, the British Railway Modelling Standards Bureau (BRMSB) was formed to develop standards for the commonly used gauges. These would take into account the improvements being constantly made to the models and toys, and were of benefit to manufacturers. It was a strange time to start such a Bureau, being in the middle of a World War. In 1950 the BRMSB published its standards, which included two track/wheelset standards for Gauge '0' with a scale of 1:43. These were Coarse, which was compatible with the Greenly Special, and Fine. The latter gave a much closer representation to scale for stock at 7mm/ft on 32mm track.

To these two, the BRMSB later added a Unified standard, that lies somewhere between the Coarse and Fine standards. Sadly for the smaller gauges the BRMSB was subsequently disbanded.

The Gauge 0 Guild is formed.

The Second World War was a watershed for '0'. In the '50s, the smaller scales became more popular and '0' went into decline. In 1956 the Gauge '0' Guild was formed to bring '0' aficionados together and to promote the gauge.

The Guild has set up its own track and wheel standards. The Guild Fine standards are compatible with the BRMSB fine. The Guild Coarse standards are slightly more refined than that of the BRMSB, but still compatible.

In the 60's the '0' gauge fraternity watched the civil war that broke out in the 4mm scale arena over track and gauge standards with the introduction of P4. There were some unpleasant exchanges of letters in the model railway press, with some members genuinely wishing to make progress, whilst others simply wished to denigrate the work of others.

In 1975 a new set of standards for 7mm Railway Modelling were published, Scale Seven. Up to that time, the approach was to take the De Facto gauge of 32mm and adjust scales around it. This gauge having been determined by manufacturers wishing to sell into each other's markets. Now a more logical approach of taking the scale as fixed and then generating the track and wheel standards to that scale was taken. This resulted in a gauge of 33.00mm. The opportunity was also used to bring in tighter tolerances. This does of course mean that there is little or nothing at present in the way of off the peg track and associated equipment to get you started. This move did generate some heated discussion, but fortunately not to the same destructive level that was experienced by the smaller scale.

As ever, the Americans are not ones to let the grass grow under their feet, and have introduced their own new fine standard, Proto48. This uses their same scale of ¼ inch/ft but its track standards are based on a gauge of 1.176 inches (29.87mm).

To complicate the picture, the Australian Model Railway Association (AMRA) and the European NEM have their own, different, track standards.

The standards (well some of them!)

Twelve recognised wheel set/track standards are as follows:

Standard Gauge Back to Back
Greenly Ordinary 32.00 mm 27.00 mm
Greenly Special 32.00 mm 28.50 mm
BRMSB Fine 32.00 mm 29.00 mm
BRMSB Coarse 32.00 mm 28.00 mm
BRMSB Unified 31.60 mm 28.50 mm
NMRA 1.25 inches
(31.75 mm)
1.118 inches
(28.40 mm)
Guild Fine 32.00 mm 29.00 mm
Guild Coarse 32.00 mm 28.00 mm
AMRA 31.87 mm 28.40 mm
Euro NEM 32.00 mm 28.40 mm
Scale Seven 33.00 mm 31.20 mm
Proto48 1.176inches
(29.87 mm)
1.091 inches
(27.70 mm)

As can be seen, most of the standards have a gauge of 32mm, the differences between the standards lie in back to back, flangeway etc measurements. I don't propose to go into the full detail, but if you wish to have this, I suggest you obtain a copy of the Gauge '0' Guild Standard Part 1 Section 1, which runs to some 30 pages.

Some of the variation in scales.

Title Scale Ratio
British 0 7mm=1ft 1:43.54
European 0 6.77mm=1ft 1:45 (Greenly)
American 0 1/4in=1ft 1:48 (6.35mm=1ft)

Does it matter?

The answer is a qualified yes. It is possible to lay track such that a variety of back to back measurements, within reason, may be accommodated. Nevertheless, a single standard between track and wheels is desirable. If you mix and match then reliable running may not be possible, in fact some standards are totally incompatible. A frequently used approach is to use only one manufacturers wheels and track. Of course a problem can then arise when that manufacturer does not produce the types of wheels that you want.

With regard to the scale variation, you should at least be aware. It is possible to mix items from the British and other scales, so long as careful placing is used. For example, a LIMA BR Mk1 carriage is 6mm narrower than one made to British '0', so a rake of these behind, say, a Britannia locomotive built to British '0' would look distinctly odd. Not only that, if you build your tunnels to US '0' then try and run a British '0' coach into it, the coach will (did) get stuck!

If you are into everything being spot on, then Scale Seven is now the main option (in the UK) .

Gauges related to '0'.

There are other gauges in this group which correspond to full size narrow and broad gauge using a scale of 1:43 ( 7mm/ft ).

BG7 is the standard used by the modellers of the Brunel Gauge, 7ft 0¼ins, which is a scale 49mm.

0n16.5 uses 16.5 mm gauge track (UK '00') which is equivalent to 2ft 4¼in. This is spot on for the Glyn Valley Tramway, but too wide for the Corris, Talyllyn, Ffestiniog and Vale of Rheidol Railways.

'EM' gauge track (18mm) gives an equivalent 2ft 6½in, which is almost spot on for the Welshpool & Llanfair, Leek & Manifold and Sittingbourne & Kemsley Railways. Anyone got any spare 'EM' wheelsets?

'TT' gauge track (12mm) is equivalent to 1ft 8½ins. 'N' gauge track (9mm) is equivalent to 1ft 3½ins. This is getting into the miniature railway realm, the latter being ideal for models of the Ravenglass & Eskdale, Romney, Hythe & Dymchurch and Eaton Hall Railways. Actually a GEM 2mm scale 28XX body kit on a Farish 8F chassis, with a few modifications, would make a very passable model of Ravenglass & Eskdale locomotive River Esk.

I am afraid there are no ready made chassis or track to suit 2ft or 3ft gauge railways at 7mm/ft. If you wish to use USA standards, 0n3 is 1:48 scale on US '00' gauge track. US '00' is 0.750ins (19.1mm) gauge, which gives a scale gauge of 3ft.


I would like to thank fellow members of the Gauge '0' Guild, particularly Phil Ellis and John Pinkney, for their help and suggestions during the preparation of this article. Assistance was also received via the Internet on the American Standards. Many in the USA sent replies to my queries, in particular Charles 'Chuck' Davis. My thanks to all for their help.


The World of Model Trains by Patrick Whitehouse and Alan Levy.
The Gauge '0' Guild Standards Manual.
The NMRA Standards Pages


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Page created by Ian Major.
Updated on Friday August 22, 1997