Two terms associated with the hobby of Railway Modelling are often confused and even used interchangeably. Whilst both describe an aspect of the model railway, often the full description relies on both for completeness. I refer to the terms Scale and Gauge.
Before World War II, very little existed in the way of standards for railway modelling and the modeller was usually tied into a single brand for consistency.
However, after the War the industry began to rebuild itself - Tri-ang for example had given their production facilities over to manufacturing the STEN Gun, with one of the Lines brothers taking the STEN Mk II and improving its design to become the Mk III - and as part of this process, the development of standards was considered.
In Britain, the British Railway Modelling Standards Bureau was formed by the then editors of Model Railway News and Model Railway Constructor along with several eminent modellers of the time. However, they were somewhat unsuccessful in achieving their goal on several counts: they had no direct links with the model railway club movement; their meetings were held at irregular intervals and unpublicised locations; they lacked the necessary 'teeth' to influence the manufacturers with most paying no more than lip service to their recommendations.
Stateside, they had more success. The NMRA (National Model Railroad Association) were also setting standards but also issued "Conformance Warrants" to show compliance and carried out checks to ensure that the manufacturer was adhering to them. Most of the manufacturers saw benefit in maintaining the Warrant for fear of losing it and suffering the subsequent adverse publicity.
In addition to the NMRA Standards, we also have the NEM (Normen Europäischer Modellbahnen) Standards instigated and maintained by MOROP (the European Federation of Model Railway Associations, the term "MOROP" is derived from "MOdellbahn" (German for "model railway") and EuROPe. NEM and NMRA work in close collaboration.
So, what has all this to do with scales and gauges?
In short, quite a lot!
After the War, most models produced were to Gauge 1 (I'll give a table with the finer details later, but let's just go over the basics for now!). As technology improved, popularity increased and costs came down, more people realised that they could afford a model railway but needed something a little smaller.
What's smaller than 1? 0 (zero!) and thus Gauge 0 was born. (Note that the Europeans still use the 0 whilst the Americans and subsequently, the British, have corrupted this to O.) As things progressed and technology improved, a further down-sizing was practical to Half 0 (i.e. H0) with OO being an adaptation to allow models of the smaller British prototypes to be manufactured at a reasonable size. Since then, things have become even smaller with the introduction of N, Z and T gauges.
Initially, it was common to refer to the likes of Hornby and Tri-ang as OO gauge or OO scale models as these were the main core products.
However, as the hobby grew, more modellers realised that they were not constrained by off-the-shelf models. Also, not all full-scale prototypes were to the Stephensonian 4'8½" gauge (The UK has the Welsh Narrow Gauge lines, Europe has an assortment of narrower and broader gauges.)
The Gauge simply defines the distance between the inner running edges of the rail. It has no influence on the size of the stock running on those rails.
Conversely, Scale defines the size of the stock and has no influence on the gauge of the track on which it runs.
Whilst there is only one way to specify gauge, i.e. as a linear distance in either metres or feet and inches, there are two commonly used ways to identify a scale: so many mm or inches to the foot (OO - 4mm to the foot) or as a ratio (OO - 1:76 scale). Putting this into perspective, at 4mm = 1ft, a six foot-high person would scale to 24mm high. At 1:76, the same would be 24.06mm high. Near enough the same, so the two forms are reasonably interchangeable.
Let's take a look at a Narrow Gauge railway, such as the Ffestiniog Railway. Their coaches have the standard 2+2 seating arrangement of a normal mainline coach so a coach scale of 1:76 would produce a reasonable model. Said railway runs on 1'11½" gauge track. At 1:76, this works out to around 7.8mm. The nearest commercial track is N Gauge at 9mm so the model would effectively be an OO Scale coach running on N Gauge track. (Incidentally, this is not a mile adrift from the commercial OO9 system.)
The following table lists an assortment (it is by no means comprehensive) of the various gauges and scales in regular use.
It is interesting to note the influence manufacturers can have on the scale – gauge relationship; in recent years, Kato have introduced models of metre gauge prototype stock to a scale of 1:150 but running on ordinary N Gauge track (referred to in the table as Nm9) and that Bemo have followed the lead by introducing models of the same prototype in H0 scale but running on H0 gauge track (H0m16) (These have yet to be adopted as standards, I believe).
In closing, I would like to thank (in no particular order) Andrew Cocker, Bill Bishop, Chis Foren, Dave Harvey, Mike Romans, and Pete Cottrell for their invaluable input from their wide base of modelling expertise.