OO gauge model railways are the most popular standard in the United Kingdom, being one of several 4 mm scale standards (4 mm to the foot (305 mm), or 1:76.2) in use, but the only one served by mass market manufacturers. OO uses 16.5 mm gauge track, which is inaccurate for 4 mm scale (it is accurate for HO scale). Many experienced modellers therefore find the OO standard inadequate, and they tend to model using the older EM gauge or the modern, exact scale P4 scale.
Double-O scale model railways were first launched by Bing in 1921 as 'The Table Railway', running on 16.5mm track and scaled at 4 mm to the foot (305 mm). In 1922, the first models of British prototypes appeared. Initially all locomotives were powered by clockwork, but the first electric power appeared in the Autumn of 1923.
OO gauge was based on HO scale (3.5 mm:1 ft (305 mm)), and kept the same gauge. However, the large propulsion mechanisms could not fit into the small British prototypes, so the scale was enlarged to (4 mm:1 ft (305 mm)) without altering the gauge.
In 1932, the Bing company collapsed, but the Table Railway continued to be manufactured by the new Trix company. However, Trix decided to use a new standard of 3.5mm to the foot or 1:87, and this scale came to be known as 'HO'. (It is thought that this may have originated as 'Half-O' gauge, but there is no proof of this.) In 1938, the Meccano Company launched a new range of OO models under the trade name of Hornby DublO, and the OO scale has remained as the UK's most popular ever since.
In the United States, Lionel Corporation introduced a range of OO models in 1938 as well. It did not prove popular and only remained on the market until 1942. OO scale was quickly eclipsed by HO scale.
The two main manufacturers of ready-to-run model railways are Hornby Railways and Bachmann Branchline, a subsidiary of Bachmann Trains. A third major manufacturer of accessories (particularly track) is Peco.
- Bachmann Branchline (http://www.bachmann.co.uk)
- Dapol (http://www.dapol.co.uk)
- Heljan (http://www.heljan.dk/)
- Hornby Railways (http://www.hornbyrailways.com)
- Lima (http://www.limamodel.com/)
- Peco (http://www.peco-uk.com)
- Dublo O gauge Association (http://www.doubleogauge.com)
- History of OO gauge (http://www.doubleogauge.com/history/history.htm)