(Last December 15th, 2012)
"Scale" relates to the ratio in size between model and prototype, expressed as some form of direct comparison. It can be expressed as a fraction (e.g. 1/76th), a ratio (e.g. 1:76) or as a statement (e.g. 4mm equals 1ft). Regardless how it is expressed, its purpose is to convey an exact dimensional relationship.
"Gauge" relates to the distance between the running rails on the track itself. There are many different gauges to be found on the world's railways but they all fall into one of three categories: broad gauge (e.g. the 7ft gauge of the early GWR); standard gauge (e.g. the current 4ft 8 1/2ins gauge of British railways); and narrow gauge (e.g. the 1ft 11 1/2ins of the Ffestiniog Railway).
Taken separately, while not exactly simple, the two terms are at least unambiguous. It is when translating it into model terms that scale and gauge sometimes become intermixed or confusing. This is largely due to a couple of things: the habit of mixing imperial and metric units with a few ratios for good measure; and the different compromises that are often made through rounding up or down otherwise awkward measurements.
The following table will help clarify the situation as well as demonstrating why the confusion arises from time to time. It shows the commonly used types of models followed by the track gauge that is normally used for models of that type when depicting standard gauge track. Following this are the two commonly used methods of describing the scale and, in brackets, the prototype track gauge that it translates into. The majority of the examples of the scale/gauge combinations shown in this table are those commonly encountered by those modeling British railways. There are also examples for those modelling European and US railways, while the overall idea will interest any modeller.
|Z||6.5mm||220:1||(4'8 1/3")||1.4mm/ft||(4'7 3/4")|
|N (Eur)||9.0mm||160:1||(4'8 3/4")||1.9mm/ft||(4'7 1/2")|
|N (US)||9.0mm||160:1||(4'8 3/4")||1.9mm/ft||(4'7 1/2")|
|2mm||9.42mm||152.4:1||(4'8 1/8")||2mm/ft||(4'8 1/2")|
|N (UK)||9.0mm||148:1||(4'4 1/2")||2.06mm/ft||(4'4")|
|TT (Eur)||12.0mm||120:1||(4'8 3/4")||2.54mm/ft||(4'8 7/10")|
|TT (US)||12.0mm||120:1||(4'8 3/4")||2.54mm/ft||(4'8 7/10")|
|TT (UK)||12.0mm||101:1||(3'11 3/4")||3mm/ft||(4'0")|
|HO||16.5mm||87:1||(4'8 1/2")||3.5mm/ft||(4'8 1/2")|
|P4||18.83mm||76:1||(4'8 2/5")||4mm/ft||(4'8 1/2")|
|EM*||18.2mm||76:1||(4'6 1/2")||4mm/ft||(4'6 3/5")|
|OO (UK)||16.5mm||76:1||(4'1 1/2")||4mm/ft||(4'1 1/2")|
|O (UK)||32.0mm||43:1||(4'6 1/5")||7mm/ft||(4'7")|
*Note: The track gauge for EM was originally 18mm. However, the current standard is considered to be 18.2mm.
Finally, apparently identical types of models are not in fact identical. For example, models in N may run on the same track in the UK, Europe and North America and may be understood to be at a scale of 2mm/ft yet the ratio in the UK, which is used by the manufacturers, differs from that of Europe and North America. A second example is HO models and OO models which also both run on the same track but which are modelled to different ratios and correpondingly different scales. It helps explain why a UK model in OO and a North American model in HO have about the same loading gauge when in reality they are quite different with the North American loading gauge being considerable bigger. This is also why UK models in OO look as if they are running on narrow gauge track which they are if you look at the calculation; a scale 7ins narrow! It is this narrow gauge look of OO that led to the development of, EM and P4, which are modelled to the same ratio and scale as OO but run on track which is closer to the correctly scaled down version.
Most of the foregoing focussed on standard gauge. For completeness, reference must be made to narrow gauge and broad gauge. Typically when one models a non-standard gauge prototype railway, one can indicate it by appending a suffix to the types described in the table. However, this too is not universal and there are at least two types of such suffixes.
In the UK and in North America, the suffix is made up of a lower case "n" followed by the prototype gauge expressed in feet. Thus, an Sn3 model railway models a prototype railway with rails 3 feet apart at a 1/64 scale.
In Europe, prototype gauges are placed in 4 categories: normal gauges (1.25 to 1.70 metre); metric gauges (0.85 to 1.25 metre); narrow gauges (0.65 to 0.85 metre), and industrial gauges (0.40 to 0.65 metre). Each non-normal category has its own suffix: "m" for metric; "e" for narrow; and "i" for industrial. Thus, H0m means a model of a prototype railway with a gauge between 0.85 and 1.25 meter at a 1/87 scale.
Now, if you were confused before, try modeling Large Scale. Unlike the relative sanity of other common scales, G Scale or Large Scale is not a scale at all, but a range of different scales where the models all run on the same track (45mm gauge, the gauge for #1 also called confusingly Gauge 1) and the scales of the models are adjusted to fit. Strictly speaking using 45mm as the gauge, a 3ft narrow gauge model should be 1:20.3 scale; meter gauge models 1:22.5 and standard gauge 1:32 (but some are scaled at 1:29 instead). 1:24 scale models should represent 42ins or 3ft 6ins narrow gauge prototypes, but this scale is often used for 36ins prototypes simply because scaling at 1/2ins to the foot is easy. Unfortunately, the majority of models available are at other scales than these: LGB is primarily 1:22.5 (due to their European meter gauge heritage); Aristo is 1:29 (due to a fudge to make models of standard gauge prototypes look better when placed next to 1:22.5 scale models); and most Bachmann cars are between 1:24 and 1:22.5. And if that's not enough confusion, there are two other "garden railway" gauges: Gauge 3 (1 1/2ins or 64mm) and Gauge 0 (1 1/4ins or 32mm). Finally, if you had a tinplate railroad as a child, it may have been referred to as O27 gauge. Those trains run on track that doesn't scale out to the real thing compared to the size of the train models, many of which were shortened versions of scale. There is nothing wrong with building a layout using this equipment if you still have it, it's still a model railroad, just not a "scale" model railroad.
And you thought only computers were perverse!
In addition the following sites may be of interest:
The Great Western Archive contains a selection of Swindon Coach Drawings and provides links for GWR locomotives and GWR Goods Wagons.
The Railway Station web site is a vast database which lists every published photo of UK stations and is the work of one man!
The UK Railway Station Track Plans site is also worth a visit.
Ah, English, the universal language - or is it? Churchill said of the Americans and the British "two great nations separated by the use of a common language" though the quote is also attributed to Shaw and Wilde. So, of course, just as boot and bonnet are articles of clothing in North America, not car parts, and a lift is what short people put in their shoes to seem taller, there are different terms to describe the same thing between the UK and North America railroads, er railways (see below). In addition there are terms that have no counterpart in North America. To reduce the confusion, and perhaps increase your vocabulary, here are some terms complied by a Canadian-born, British modeller:
|British term||North American term||Notes|
|bogies||trucks||not to be confused with the British term below|
|brake van||caboose||now obsolete with End of Train devices|
|buffers||no real equivalent||some end-of-track stops have a buffer, mostly in stations|
|buffer beam||cow catcher or pilot||Not a strict translation as early North American locomotives had cow catchers for that purpose, while British railways are required to fence their right of way, ergo no strays and the loco only needed something to hold the buffers and coupler.|
|carriage||coach or passenger car||A carriage here would be a pram there!|
|driver||engineer||not to be confused with a P. Eng.|
|earth||ground||electrical, not dirt in the garden|
|goods van||box car|
|guard||conductor||person not electrical|
|horse or cattle van||cattle car|
|lorry||truck||a road vehicle|
|mains||circuits||for household current|
|mineral wagon||gondola||usually steel sided|
|plank wagon||wood sided gondola|
|Plastikcard||Styrene||Both are trademarked names.|
|points||turnout||The prototype calls them switches but modelers use turnout to distinguish them from electrical switches.|
|private owner wagon||privately owned car|
|railway||railroad (US)||the company - Canadian usage follows the British|
|railroad||railway (US)||the physical plant/track etc. - Canadian usage follows the British|
|railway modelling||model railroading|
|shed||depot/roundhouse||as in engine shed.|
|shunting||switching||shunting is also used mostly for small moves.|
|signal box||signal tower or interlocking tower|
|sleepers||ties||the bits that support the rails|
|trainspotter (anorak)||railfan (railway nut)|
|tram||streetcar||some properties called them trams, e.g. Halifax, N.S.|
|trucks||freight cars||Trucks in N. America are the UK's lorries or the UK's bogies|
|wagons||gondolas/open top RR freight cars||A wagon in N.America is a child's toy or a pioneer's mode of horse-pulled transport.|
|Underground||subway||as in urban tranist system.|
There are more comprehensive sources of terminology web pages gleaned from our experience:
Wikipedia Glossary of UK railway terminology
To reduce the confusion and increase your vocabulary check this one.
|Country||Track Gauge||Track Gauge|
|Costa Rica||3ft 6in||1.067m|
|East Africa||3ft 3.75in||1.000m|
|El Salvador||3ft 0in||0.914m|
|New Zealand||3ft 6in||1.067m|
|Saudi Arabia||4ft 8.5in||1.435m|
|Sierra Leone||2ft 6in||0.762m|
|South Africa||2ft 0in||0.610m|
|South Africa||3ft 6in||1.067m|
|United Kingdom||2ft 0in||0.610m|
|United Kingdom||2ft 6in||0.762m|
|United Kingdom||3ft 0in||0.914m|
|United Kingdom||4ft 8.5in||1.435m|
|West Africa||3ft 3.75in||1.000m|
|West Africa||3ft 6in||1.067m|
|Western Australia||3ft 6in||1.067m|
A question that comes up time and time again realtes to track compatability between models from different manufacturers and also from the same manufacturer over time. In theory, since OO models and HO models share the same track gauge, it should be possible to run any OO equipment on any OO or HO track. However, in practice this is not necessarily true because of the different flange depth, flange width and back-to-back wheel measurements stock used by the various OO locomotive and rolling stock manufacturers and the different track height and switch dimensions used by the various manufacturers of OO and HO track.
It is certainly true that the manufacturers of ready-to-run British trains in 00 scale have used a bewildering assortment of wheel and track dimensions approximating H0 gauge, particularly prior to about 1970. If one were to produce a complete cross-reference of all the brands, with compatibility ratings, it would be a wonderful effort but I am afraid it might be a bit beyond most of us individually. However, as long ago as (I think) 1971 it was possible to say that all the major 00 RTR manufacturers bar one were using one of the two H0 gauge standards for their products. So for equipment made in the last 30 years or so, the sets of dimensions have been simplified to 3 choices: NMRA H0, NEM H0, and Hornby. Of course this ignores the specialist firms producing wheels and track in the "true" 00 gauges between 18mm (original EM) and 19mm (rare US 00), but this discussion is really not intended for people working to those finer standards.
What follows is a collection of observations based on many brands of locos and rolling stock and a few brands of track.
Locos and stock by Airfix (GMR), Palitoy Mainline, Replica, Dapol and Bachmann (U.K.) have NMRA standard (S-4) H0 wheels. (Some early wheels from Airfix and Mainline are undergauged but can be adjusted. Avoid stock having plastic wheels cast in one piece with the axle).
Locos and stock by Lima, Trix and Joueff (and British H0 rarities by Fleischmann and Marklin) have NEM standard H0 wheels, which are similar in many respects to NMRA wheels but have much deeper flanges.
NMRA wheels will operate on NMRA standard track, code 75 and up. NEM wheels will operate on NMRA standard track, code 100 only, and on NEM standard track (I assume!). NMRA standard (S-3) track includes all the popular H0 brands sold in North America for "domestic" model trains, including Atlas, AHM (Casadio) and Shinohara. The Shinohara turnouts have their clearances on the tight side of the standard and require that wheels be adjusted exactly to the standard back-to-back distance of 14.4mm, as Bachmann wheels are. Peco Streamline code 100 almost conforms to NMRA S-3 but its clearances are slack, thus the flangeway gaps around frogs are theoretically a bit too wide. However, there are several layouts where standard H0-gauge equipment runs without trouble on Peco Streamline, so perhaps the theory (of tread widths and flangeways) can be overlooked in this case.
And now Hornby. Hornby wheels and track, and even more so the ancestral Triang and Rovex, have alas never conformed to a standard. This is especially unfortunate because it has led to a perception among N.A. dealers and hobbyists that British 00 trains will not run on H0 track, and require special "British 00 track", which as we have just seen is generally not true. It cannot have been good for British exports, surely. Be that as it may, Hornby locos and stock can safely be used with Hornby track, or probably Peco Setrack which appears to be made to the same dimensions. Some recent Hornby locos can be operated on Peco Streamline, but it is really not a reliable combination. Peco plastic wheels were closer to Hornby dimensions than to the standard: they were used in kit-built stock.
Of the major departed brands, Hornby-Dublo 3-rail was naturally a thing unto itself, the gauge being 5/8 inch rather than 16.5 mm., and Hornby-Dublo 2-rail was similar. Wrenn, who continued part of the Hornby-Dublo range, used wheels of the NEM standard type.
The foregoing simplifies things in terms of standards and much of the detail has been glossed over because of lack of data. Will Lima stock (NEM) run on Fleischmann track (NEM)? Should do, but ......
A good beginning for the modeller would be to choose one of the 3 main groups for a "standard" and to acquire only stock which belongs in that group, changing the wheels on anything which is deemed "non-standard" as a result of the choice. For example, Bachmann/NMRA or Hornby/Setrack. BRMNA member-suppliers may be able to advise on the supply of replacement British wheels, e.g. Romford drivers. Peco Streamline track is quite generally available and may provide the widest degree of compatibility with the two H0 Standard groups.
More recently, Hornby have upgraded their production standards significantly, and their rolling stock is now provided with wheels which conform to NMRA S-4. Currently (2004) the producers of ready-to-run OO scale models in British outline are Bachmann, Dapol, Heljan and Hornby, and they all use NMRA standard wheels so that recently-produced models will run on standard track, both code 100 and code 75.