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Model Railway, what is OO Gauge?

January 29, 2013

OO gauge (OO scale)

The OO gauge or OO scale (also spelled 00 gauge and 00 scale) model railroads are the most popular standard gauge model railroad tracks in the U.K. This track gauge is one of several 4mm-scale standards (4 mm:foot / 304.8 mm or 1:76.2) used, but it is the only one to be served by the major producers. Despite this, the OO track gauge of 16.5 mm (0.650 in) is inaccurate for 4mm scale, other gauges of the same scale have arisen to better serve the desires of some modellers for better scale accuracy.


Origin and History

Double-0 scale model railroads were launched by Bing in 1921 as ‘The Table Railway’, running on 16.5 mm (0.650 in) track and scaled at 4mm to the foot. 1922, the first models of British prototypes appeared. Initially all locos were powered by clockwork, but the first electric power appeared in autumn 1923.



OO describes scale models with a scale of 4mm = 1 foot (1:76) running on HO scale 1:87 (3.5mm = 1 foot) track (16.5mm/0.650″). This combination came about as early clockwork mechanisms and electric motors were difficult to fit within HO scale models of U.K. prototypes which are smaller than equivalent European and USA locos. A cheap and quick solution was to enlarge the scale of the model to 4mm to the foot but keep the 3.5mm to the foot gauge track. This allowed more space to model the external valve gear. Resulting HO track gauge of 16.5mm represents 4 feet 1.5 inches at 4mm to the foot scale, this is 7 inches under scale or is approximately 2.33mm too narrow.


1932 the Bing company collapsed, but the Table Railway continued to be produced by the new Trix company. Trix decided to use the new HO standard, being approximately half of European O scale (1:43 scale).


1938, the Meccano Company launched a new range of OO scale models under the name of Hornby Dublo, OO gauge remained the UK’s most popular scale/gauge ever since.


In the United States, Lionel Corporation introduced a range of OO gauge models in 1938. Soon other companies followed but it did not become popular and remained on the market only until 1942. OO gauge was quickly eclipsed by HO gauge. The Lionel stock of OO used 19mm/¾” track gauge, a scale 57″, a track width which was more to scale. There is a small following of North American OO scale/gauge today.

our OO (00) scale Figures


The Scaling

16.5 mm (0.650 in) gauge at 4 mm:1-foot means that the gauge represents 4 ft 1 1⁄2 in (1,257 mm), 7 inches (178 mm) narrower than the prototype 4 ft 8 1⁄2 in (1,435 mm). This noticeable difference are aggravated if over-scale rail section, over-scale wheel width and deep wheel flanges are used on typical scale models. These departures from scale require much larger clearances on pointwork and are particularly noticeable when you are looking along the track. This model scale gauge more accurately represents the narrow gauge railways built to 4 ft  (1,219 mm) gauge, for example the Padarn Railway and Saundersfoot Railway in Wales and the Glasgow Subway of Scotland.


Though they run on the same track, OO gauge and HO gauge models of the same prototypes do not fit well together since the OO models are larger than the HO equivalent.


OO gauge is also used to represent the 5 ft 3 in (1,600 mm) Irish gauge, where it is a scale 131⁄2 inches (343 mm) too narrow.


These differences have led to the development of finescale standards EM gauge and P4 scale.

OO Scale/Gauge
OO Scale BR 25054.JPG
U.K. prototype model of a 00 scale (1:76) British RailClass 25 shown with a 22mm-One pound coin for scale
Scale per foot: 4 mm to 1ft
Scale ratio: 1:76.2
Gauge: 16.5 mm (0.650 in)
Prototype Gauge: Standard gauge

OO gauge today

OO remains the most popular scale for railway modelling in the U.K. This is most likely attributable to a ready availability of ready-to-run stock and starter kits. Ready-to-run in the United Kingdom is dominated by Hornby Railways and Bachmann Branchline. Other sources of ready-to-run rolling stock or locos include the Dapol, Heljan, Peco, ViTrains and previously Lima. Other scales, with the possible exception of N gauge, lack the variety and affordability of UK ready-to-run products, it is likely that this deters British modellers and leads to the prevalence of OO gauge.


Good results in OO gauge can be achieved despite the scale inaccuracies with modern ready-to-run equipment on ballasted Code 75 trackwork. With realistic track spacing (the “6-foot”), and try to minimise or hide tight curves when necessary.


4 mm finescale standard

Many experienced modellers find the OO gauge standard produces a “narrow gauge” appearance when the model is viewed from head on. Greater accuracy is possible using either EM gauge or the closer to exact P4 gauge track.


Flextrack is available for both EM and P4 gauges (from manufacturers such as C&L Finescale, SMP and The P4 Track Company), ready-to-run (RTR) point and crossing (P&C) work is not available. This trackwork must be constructed by the modeller. Kits are also available from the aforementioned sources amongst others. Several of these kits are also available for the OO gauge modeller who aims for more realistic track, since most RTR track is actually scaled to HO and does not represent any British prototype and the sleeper spacing is too close together for scale. EM gauge has slightly overscale flanges and flangeways on point and crossing works.
P4 is closer to scale but the smaller flanges and flangeways on P&C work expose poor track construction.


Hornby Flying Scotsman locomotive on an 00 gauge layout

OO gauge Model Railway of the Sapsan Railway from Moscow – Saint Petersburg Railway and Moscow to Nizhny Novgorod Railway in the Museum of the Moscow Railway.

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