Standard wire gauge

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 1 March, 1884, by the British Board of Trade. SWG is not to be confused with American wire gauge, which has a similar but not interchangeable numbering scheme. == Standard ==

A table of the gauge numbers and wire diameters is shown below. The basis of the system is the thou (or mil in US English), or . Sizes are specified as wire diameters, stated in thou and tenths of a thou (mils and tenths). The wire diameter diminishes with increasing size number. No. 7/0, the largest size, is (500 thou or ) dia., No. 1 is (), and the smallest, No. 50, is ( or ). The system as a whole approximates an exponential curve, plotting diameter against gauge-number (each size is a approximately a constant multiple of the previous size). The weight per unit length diminishes by an average of approximately 20% at each step. Because the weight per unit length is related to the cross sectional area, and therefore to the square of the diameter, the diameter diminishes by approximately 10.6%: :\mbox{Diameter Ratio} = 1-\sqrt{1-0.2} \approx 10.6\% However, the system is piecewise linear, only approximating the exponential curve loosely. Thus, it runs in constant steps of () through the range No. 49 - No. 39 and of () through No. 39 - No. 30. ==See also==