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Model railways in solihull
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29 October 2021


Why Model in OO Gauge?

The Bad News - Track Gauge


I describe 'OO' as a gauge rather than a scale for a very good reason. You cannot call it a scale when one of the fundamental components is by definition not to scale. This component is the track. The 'gauge', or distance between the inside edges of the rails, is 16.5mm in 'OO', which equates to 4 feet and 1.5 inches at the nominal 'scale' applied to 'OO' of 1:76 or 4mm:1 foot. The correct British standard gauge for railways since Victorian times is 4 feet 8.5 inches, or about 18.83mm in 'OO'. This is represented by the niche scale known as 'P4' which has this correct gauge and closer to scale wheel standards and track. Another problem with 'OO' is that it is usually 'coarse scale' in that the rails are deeper and wider than they should be to allow for correspondingly deeper than scale flanges on rolling stock wheels that give better running on less than perfect track with very tight curves.


Having said that, 'OO' is a lot finer than it used to be before about the 1970s and some modellers use much finer rails and wheels with closer-to-scale flanges, similar to 'P4' standards, but still with the wrong gauge. Some people say that the difference in gauge is not very noticeable, but if you look at a 'P4' layout, the 2.33mm difference is surprisingly noticeable. A compromise is 'EM' which has an 18.2mm gauge.


The gauge was a kind of accident where someone decided to model rolling stock at 1:76 scale and the closest to scale track available was continental 'HO' (or half 'O'), at 1:87. A useful side-effect of this is that there is more clearance for outside motion on steam locomotives, but at the same time there is less clearance for motors and transmissions between the chassis frames.

The Good News - Size


'OO' is large enough so that modellers do not need to be watchmakers to build rolling stock kits or detail stock, but it is small enough that you can have a layout where you can run full length mainline trains in one room or the loft of a small British house.


More Good News - Availability


'OO' is effectively the standard ready-to-run gauge in Britain, probably largely due to Hornby's many years of production, despite their occasional financial scares, making them a household name synonymous with model railways. Indeed, when I have occasionally worked in Bob's Models in Solihull, some customers describe themselves as owning 'a Hornby' if they have a trainset, even if Hornby was not the manufacturer. Over the years other manufacturers have come and gone, but Bachmann and Hornby are probably the two largest suppliers of British ready-to-run model railway items today and between them and with the addition of smaller suppliers such as Dapol and Heljan, a very wide range of model railway rolling stock dating mainly from about the 1920s to the present day is now available.


This long term production, wide range, the many manufacturers and the fact that the hobby has been from time to time one of the most popular in Britain means that there is a vast amount of second hand rolling stock available at shops, toy fairs and on e-bay in addition to all the new items. Since the 1970s and 1980s, many of the offerings that have been produced are very close to scale and only require some detailing work to make them accurate models. Recently introduced models are supplied so well detailed and sometimes ready-weathered that, if you wanted to, you wouldn't have to change them at all to own an excellent model.


In addition to this large amount of ready-to-run rolling stock there is also a vast range of rolling stock kits from many manufacturers for the more adventurous modeller.

Still More Good News - Interchangeability


Within reason, all the British ready-to-run manufacturers' products produced over the last 30 years will run on the same track using the same controllers and will couple together completely without modification. Having said that, it is always wise to aim to have similar widths and heights of couplings on all vehicles and similar length hooks to minimise derailments. An alternative would be to fit 3-link or screw couplings to all your rolling stock which gives standardisation and removes the need for the ugly tension-lock couplings all current ready-to-run models are supplied with. All available ready-to-run rolling stock has wheels of similar widths with similar sized flanges and runs on a nominal 12 to 18 Volts Direct Current supply.


Kit built products often come with their own wheels and couplings and these will also run on the same track and couple to ready-to-run rolling stock, but they are better fitted with easily-available Jackson metal wheels if these are not supplied, and suitable standardised couplings.

Yet More Good News - Price


Ready-to-run rolling stock has become more expensive in recent years, partly due to the fact that it is often better detailed and runs better than items from just five or ten years ago. Excellent models of large steam locomotives can be bought for under 100 pounds and diesels for under 60. Second hand locos which are still good models can be bought from around 25 pounds. New Items cost about the same as they do in 'N' gauge, despite 'OO' being nearly twice as large in terms of the scale. There are few 'O' gauge ready-to-run items and what is available is usually built from a kit and as such costs hundreds of pounds per locomotive.


This low cost means that you can gradually build up a large collection if you want to without it costing a fortune.



'OO' model railways can be anything you want it to be. You can commission someone to build expensive etched brass rolling stock kits and finescale kit-built track if you want to or you can buy cheap second hand ready-to-run items from a toy fair and run them un-modified. You can mix kits and modified ready-to-run, perhaps with a little scratch-building as I do to produce (hopefully) reasonably accurate models at low cost and run them on the same track as a brand new 70 pound Bachmann or Hornby steam locomotive and all the items you run can be good models and perhaps weathered also. Friends can bring models round to run on your layout with no modifications required.


If you are new to the model railway hobby, there is little question that it would be a wise move to start with an 'N' or 'OO' gauge train set. The same is not currently available in 'O' gauge and if it was, it would be a lot more expensive. The added size of 'OO' models means they are intrinsically more robust than 'N' gauge ones, which is a major issue if small children are in the house.




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© Solihull Model Railway Circle 2000-2024. Whilst every care has been taken in the preparation of this website the publisher, Solihull Model Railway Circle, cannot be held responsible for the accuracy of the information contained in the website, nor for any consequence arising from such information. The articles included and the views expressed on this website are those of the writers and do not necessarily reflect the views of Solihull Model Railway Circle or its members or advisors. This website is intended to be a resource, but initially it is for promoting the Solihull Model Railway Circle.