Wire thickness is a measure of the diameter of a wire, and is typically expressed in either millimeters or inches. The two most common terms used to describe wire thickness are MIL and GAUGE. MIL stands for 'milli-inch' and is a unit of measurement equal to one thousandth of an inch. GAUGE is a unit of measurement that is based on the number of times a wire needs to be passed through a draw plate in order to reduce its diameter by one unit.