What Gauge does Hornby use?

What Gauge does Hornby use?


One of the biggest confusions in model railways is over gauge/scale and how to pronounce / write OO.

So what actually is OO Gauge ?  How do you say it?  How do you write it ?

And what gauge does Hornby use ???

Follow our explanations below and all will become clear… 


Table of Contents

  • What actually is OO Gauge?
  • Isn't 4mm Scale and OO Gauge all the same?
  • Why are there two additional gauges?
  • Is it OO or 00 ?
  • What gauge does Hornby use?


What actually is OO Gauge?

In 1891, at the Leipzig Toy Fair, the large German Toy Maker,  Märklin, defined and presented gauges 1-5 as standards for toy trains. Märklin then followed up these with 0 gauge, and another German toy firm, Bing, brought out trains which were half as big as 0 Gauge, called Double 0.



This new gauge was on a track of 0.625 in, which equates to 16.5mm. However, Bing's OO gauge at 4mm scale became a British standard, larger than the 3.5mm scale on the same gauge of track favoured elsewhere in Europe and the US.

So OO gauge is a track width (between the rails), of 16.5mm and the rolling stock, buildings, etc., are at a scale of 4mm/1ft.

But, at a scale of 4mm/1ft, the track width of 16.5mm is actually too narrow to be a true representation of the prototype track.

Isn't 4mm Scale and OO Gauge the all the same?

No, because there are two other gauges commonly used in 4mm scale modelling. Both of these are favourites of the more advanced modellers, as they give a far more accurate look to the trackwork. These are EM, which is a gauge of 18mm, and P4 which is 18.83mm.

To clarify:

  • Gauge refers to the distance between the rails
  • Scale refers to the size of the model when compared to the prototype.  For example, 4mm/ft means every foot in reality is equivalent to 4mm on the model
  • Ratio is the different in size between the model and the prototype. The Scale of 4mm/ft is a Ratio of 1:76.2.

So 4mm scale has 3 different ‘standard gauge’ track dimensions.

Why are there two additional gauges?

For EM gauge,  it is possible to move the wheels out on an axle from 16.5mm to 18mm, without having to do any or very little ‘surgery’ on the loco or wagon chassis. This is mainly because the trains are manufactured to run on ‘train set’ curves, which require significant amounts of ‘sideplay’ in the wheelsets. Because EM gauge track is usually laid with far more gentle curves than Set Track, the reduction in side-play is compensated for by the lack of sideways movement required. 

P4 gauge, at 18.83mm, is an accurate, scaled-down version of the 4ft 8½" track used on Britain's standard gauge railways.  However, it's not usually possible to push wheels out that far, within ready-to-run chassis, so again the more advance modeller will often  make loco and wagon chassis from kits or scratch build to obtain the dimensions required.   

Is it OO or 00?

Hornby Dublo model railways & diecast from Hattons Model Railways

To be precise, it should always be 00 (two zeros).  But, O gauge is known as Oh Gauge, not Zero Gauge, so OO gauge is referred to as as Double Oh  (or in Hornby's early 20th Century parlance ‘Dublo’).

Simon Kohler, who was until recently Hornby's Marketing & Development Director, is quite adamant that it should always be called, mentioned, written, breathed as Double Zero.

However, despite the double zero being the correct term, double letter O is a far more common search internet term.

What gauge does Hornby use?

From the information above, it should be fairly obviously that Hornby uses OO gauge, which is 16.5mm track with and a scale of 4mm/1ft.


Except, Hornby now also sell TT120 gauge….. which is a whole different story.

Hornby TT:120 Catalogue | Hornby UK



Happy modelling

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