Electric Guitar StringsThe gauge of an electric guitar string is defined as the thickness of a guitar string. It is generally used for steel strings. The dimensions are in inches. The designation. 010 means e. g. 0.01 inches or 0.25 mm. To define the gauge of the entire string set, usually the thickness of the highest string is used. So a set of 10's is a set, where the high e string is 0.010" thick and the remaining strings are fitting gauges.