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OO
OO scale model of a British Rail Class 25 shown with an 18 mm coin for size.
Scale per foot:	4mm to 1ft
Scale ratio:	1:76.2
Gauge:	16.5mm
Prototype Gauge:	Standard gauge

OO gauge or 00 gauge model railways are the most popular standard in the United Kingdom. It is one of several 4 mm scale standards (4 mm to the foot (304.8 mm), or 1:76.2) in use, and the only one served by mass market manufacturers. 00 uses 16.5 mm gauge track, which is inaccurate for 4 mm scale.

Contents 1 History 2 OO today 3 4 mm Finescale Standards 4 See also 4.1 Related scales 4.2 Manufactures 5 External links

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

OO scale uses the same track gauge as H0 gauge (3.5 mm to the foot, 1:87). However, the large propulsion mechanisms could not fit into the small British prototypes, so the scale was enlarged to 4 mm to the foot without altering the gauge. This means that the scale gauge represents 4'1½", seven inches narrower than the prototype 4'8½". It is also used to represent the 5' 3" Irish gauge, where it is a scale 13½ inches too narrow. These noticeable differences are aggravated by the over-scale rail section, over-scale wheel width and very deep wheel flange. These departures from scale require much larger clearances on pointwork and are particularly noticeable when looking down the track.

In 1932 the Bing company collapsed, but the Table Railway continued to be manufactured by the new Trix company. Trix decided to use the new H0 standard, being approximately half of 0 gauge (1:48 scale).

In 1938, the Meccano Company launched a new range of 00 models under the trade name of Hornby Dublo, and 00 gauge has remained the UK's most popular ever since.

In the United States, Lionel Corporation introduced a range of 00 models in 1938 as well. Soon other companies followed but it did not prove popular and remained on the market only until 1942. 00 gauge was quickly eclipsed by H0 scale.

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To this day OO remains effectively the dominant scale for railway modelling in the United Kingdom; this is most likely attributable to a ready availability of ready-to-run stock and starter sets. This particular area in itself is effectively dominated by firms such as Hornby Railways, and Bachmann Branchline, a subsidiary of Bachmann Trains. However, other sources of ready-to-run rolling stock include the Wales-based firm Dapol and Peco. Other scales, with the possible exception of N gauge, lack the variety of ready-to-run products, and it is likely this that deters British modellers and leads to the prevailance of OO.

Many experienced modellers find the 00 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 scale P4 gauge track.

Whilst flextrack is available for both EM and P4 gauges^{[citation needed]}, ready-to-run (RTR) point and crossing (P&C) work is not available, so P&C trackwork must be constructed by the modeller. Kits for doing this are available from sources such as C&L Finescale, Marcway, SMP and the P4 track company. Several of these kits are also available for the OO modeller who aims for more realistic track, since most RTR track 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 work; P4 is closer to scale but the smaller flanges and flangeways on P&C work expose poor track construction.

• OO9 - Used for modelling 2 ft narrow gauge railways in 4mm scale
• OOn3 - Used for modelling 3 ft narrow gauge railways in 4mm scale
• HO - 3.5mm scale using the same 16.5mm gauge track as OO.
• EM - 4mm scale using 18.2mm gauge track.
• P4 - A set of standards using 18.83 mm is accurate for 4mm scale.

• Bachmann Branchline - One of the largest manufacrures of ready to run OO
• Dapol - Produce kits and ready to run wagons
• Heljan - Produce a small number of locomotives and wagons
• Hornby Railways - One of the largest manufacturers of ready to run OO
• Lima - Produced budget OO ready to run, bought by Hornby
• Peco - Produce a wide range of track

• Willets Scale Models, Specialist manufacturer in 4mm scale railway stock.
• Double O gauge Association
  • History of OO gauge