00 gauge or 00 scale model railways are the most popular standard-gauge model railroad tracks in the U.K. This track gauge is one of several 4mm-scale standards (4mm:foot (304.8mm) or 1:76.2) used — the only one served by manufacturers; 00 gauge track is 16.5mm gauge, which is inaccurate for 4mm scale. The name is also often written OO scale with the letter instead of the number, not recognising that the name is a progression from the earlier 0 gauge, 1 gauge, 2 gauge and 3 gauge.
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.
00 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.
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 European 0 gauge (1:43 scale).
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.
16.5mm gauge at 4mm:1 foot means that the scale gauge represents 4ft 1½in, seven inches narrower than the prototype . These noticeable differences are aggravated by the over-scale rail section, over-scale wheel width and deep wheel flanges used on many models. These departures from scale require much larger clearances on pointwork and are particularly noticeable when looking along the track. This scale gauge more accurately represents the narrow gauge railways built to gauge, for example the Padarn Railway and Saundersfoot Railway in Wales and the Glasgow Subway in Scotland.
Though they run on the same track, 00 gauge and H0 gauge models do not sit well together since the British models are larger than their European or American counterparts, when the reverse ought to be the case.
00 is also used to represent the Irish gauge, where it is a scale 13½ inches too narrow.
Good results in 00 can be achieved despite the scale inaccuracies if one uses more modern ready-to-run equipment on ballasted Code 75 trackwork (e.g. Peco Streamline), with realistic track spacing (the "6 foot"), and try to minimise or hide curves where necessary. Most finescale modellers began in 00, developed their skills and advanced to finescale.
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 (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, so P&C trackwork must be constructed by the modeller. Kits for doing this are also available from the aforementioned sources amongst others. Several of these kits are also available for the 00 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.