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What is an OO Gauge Model Railway and other OO Gauge Questions


Although OO gauge has been around for many years, it regularly comes up in questions and is often subject to criticisms. I have worked with OO gauge most of my life apart from a short time with N gauge and also in HO when I built a small American based layout. So while there are many qualified people to speak on the subject, I thought my non partisan, user friendly Q&A might be appropriate and well received.

Railway modelling is a very satisfying hobby in any size gauge. I hope you enjoy my insights.

Please note all photos are taken by the author from his own model railway.

OO Gauge Layout


What is an OO gauge model railway?

More than anything else, OO gauge is a legacy scale that now dominates the UK market. To compare, O gauge scale is 7mm to a foot, HO (Half O) is 3.5mm.

At 4mm to a foot, OO gauge came about because early British clockwork motors would not fit neatly into their HO bodies. Standard British steam locomotives are generally smaller than their European and American cousins. OO gauge thus became established and the rest is history.

OO gauge implies that one foot of standard locomotive becomes 4mm of model size. This can then be run on a normal household tabletop layout of 4ft by 6ft, the starting size of most childhood train sets.

What scale is OO gauge?

OO gauge is the standard railway modelling gauge used in Great Britain. It is also known as 1:76 or 4mm to one foot. This means every one foot size of the original item is scaled down to 4 millimetres or 1/76th of the original.

What size is OO gauge?

As mentioned above, OO gauge is 1/76th the size of the original item. This can be a steam engine, diesel, station or urban buildings. OO gauge is often seen as being a diorama and with most people standing between five and six feet, the people of this little land tend to be about 2 cm tall.

OO gauge diorama


Is OO gauge the same as HO?

The simple answer is no. HO is 3.5mm to one foot. Much of the global market is based upon HO and this is a huge business in Europe and North America. Seen separately OO and HO models appear similar but put two locomotives close together and the size difference becomes apparent.

At one time, I used to buy model people and chairs and other extras to populate my layout. Some items were only available in HO from European suppliers. But these days there is a good supply in OO aswell and I have replaced everything. The keen eye can spot the difference and it just doesn't sit well.

Can OO gauge run on HO track?

Technically there is no OO gauge track being massed produced. It is a specialised product. All HO and OO rolling stock run on HO track for expediency and cost factors. The difference is only 7 inches and while OO gauge look slightly too big, it has been entrenched for a long time and doesn't impact the market forces.

So yes, OO gauge engines run on HO track.

Ballast Spreader


How to ballast OO gauge track

Ballast comes in packets and there is no set way to ballast your track. You can sprinkle with your fingers or spoon in like sugar into a cup of coffee.

However for a more even spread, I have built little plastic box. It sits on grooves over the two rails and is narrow at the bottom. Moving the box along the track allows a steady flow of ballast on to the trackbed.

See above photo. There are 2 notches at the base which allows the unit to sit on the track. The floor inside is sloped diagonally to create a shute.

In all the cases above I then use a small paintbrush to smooth out any lumps or bumps.

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How to clean OO gauge track

All model railway track attracts dirt that builds up on the metal surface. The problem is twofold. First the ability to conduct electricity from the rails to the electric motor is reduced and the model could stagger or even stop. Second the wheels can trasfer the dirt from the rails up into the motor and reduce performance or even damage the mechanism.

There are a couple of ways to clean the track. I use a spirit soaked rag and wipe the metal surfaces but there are also some special rubbing tools provided by various manufacturers. In the past there have also been some purpose built track cleaning wagons that cleaned the track as the train ran. The best of these was a heavy black coal wagon made by Hornby Dublo. In my view this has never been improved on. Sadly these wagons sell on eBay for upwards of £400.


How to clean OO gauge wheels

This is not an easy question to answer. Model locomotives can be cleaned by spinning the wheels on an electric brush. However wagons have nothing to make the wheels turn.

The good news is that most modellers have a finite number of wagons and I simply use a modelling knife and turn the wheels with my fingers. I then repeat the spin with a spirit soaked rag.

In the United Kingdom, OO gauge is by far the most popular but worldwide it is the slightly smaller HO gauge. So the UK is somewhat of an anomaly. For those with less room, N gauge is popular and at the other end O gauge is making a comeback.

I also think this choice is somewhat subjective. If you are passionate about N gauge you may not see this answer in the same light.


How to lay OO gauge track

There is one way to lay any gauge track. Afix with proper size tacks to a hard wooden surface. Anything that is softer, like some chipboards, will allow fibres to rise into the motor. Above all do NOT lay track on the floor or on to any kind of carpet. Carpet is full of loose fibres and furthermore the trackbed would never be stable. Flooring by its very nature is the place where dust and fibres collect. Neither of these situations is good.

I remember when I was young, I had a clockwork engine and I layed the track under all the dining room tables and chairs. It didn't matter because it was a toy although I doubt if the clockwork engine appreciated my cavalier attitude. Remember, your OO gauge locomotive is not a toy, it is very often expensive and relatively fragile. Proper care will give you many years of enjoyment.

What size ballast do you need for an OO gauge layout?

Downsizing a lump of ballast by 4mm for each foot could possibly be an exercise in futility. I am sure manufacturers use various size scieves until the size looks right. I have a collander that used to boil brocolli and produces a nice size ballast for wagon loads. I am sure I could mess around and make a realistic track ballast.

OO gauge scenery, cars and coffee shops


How do gauge sizes work?

Gauges are the length in the real world that would be represented by the respective length in the model world. O gauge is also known as 7mm and this means every foot becomes 7mm in the model (I always thought it odd that the archaic 'foot' is used to calculate the decimal millimetre). HO, or half O is 3.5mm and OO is 4mm.

Please note there is no OO track. OO and HO both run on HO track and anyone with a really good eye may notice that the OO locomotives and rolling stock are slightly oversized.

© 2020 Christine and Peter Broster


Christine and Peter Broster (author) from Tywyn Wales UK on April 13, 2020:

Hello Allan. Yes the photos are all from my own layout. I recently reballasted the whole railway to give it a fresh look. Then spent even longer running all the engines to find the spots where a little brushing was needed. Very often when I do an article I collect my own thoughts and ask myself, is this something I would like to know, Yes I love going to exhibitions and I enjoy the simple and the complex layouts. As long as the hobby survives, I am happy. Very curious if covid 19 has garnered some new enthusiasts. I got the idea for my bin out of the railway modeller years ago. It has been a real time saver. All the best Peter.

Alan R Lancaster from Forest Gate, London E7, U K (ex-pat Yorkshire) on April 13, 2020:

Hello Christine and Peter, this could be a useful beginner's tutorial for anyone who wishes to embark on OO Gauge modelling.

I've been a member of the Double O Gauge Association (DOGA) for a number of years - this year's been pretty trying, with all exhibitions off for the duration so we 'live' online, including fellow members of DOGA swapping tips or anecdotes on the Forum while we can't meet at shows or at meetings - and when I'm at shows I visit a lot of beginners' and advanced modellers' layouts. Are the images here of your own layout? It's a simple, straightforward example of railway modelling. Textbook you might say. keep up the good work.

PS For ballasting I use Poppy's ballast bin, similar to yours but made in balsa. comes in kit-form for self-assembly

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