<P> British Standard Wire Gauge is a set of wire sizes given by BS 3737: 1964 (now withdrawn), and is generally abbreviated to SWG . It is also known as: Imperial Wire Gauge or British Standard Gauge . Use of SWG sizes has fallen greatly in popularity, but is still used as a measure of thickness in guitar strings and some electrical wire . Cross sectional area in square millimetres is now the more usual size measurement for wires used in electrical installation cables . The current British Standard for metallic materials such as wire and sheet is BS 6722: 1986, which is a solely metric standard . </P> <P> SWG was fixed by Order of Council August 23, 1883 . It was constructed by improving the Birmingham Wire Gauge . It was made a legal standard on March 1, 1884 by the British Board of Trade . SWG is not to be confused with American Wire Gauge which has a similar but not quite interchangeable numbering scheme . </P> <P> The basis of the system is the thou (or mil in US English), or 0.001 in . No. 7 / 0, the largest size, is 0.50 in . (500 thou or 12.7 mm) in diameter, and the smallest, No. 50, is 0.001 in . (1 thou or about 25 μm) in diameter . The wire diameter diminishes with increasing gauge size . Between each gauge, the weight per unit length diminishes by approximately 20% . Because the weight per unit length is related to the area, and therefore the square of the diameter, the diameter diminishes by approximately 10.6%: </P>

Difference between american wire gauge and standard wire gauge