The term 'Inch Fractions' refers to a system of measurement used in the United States and other countries. It is based on the imperial system, which uses inches as its unit of measurement. The term 'Mils' is an abbreviation for 'millimeters, ' which is a unit of length equal to one thousandth of a meter. In this system, fractions of an inch are expressed in mils, with one mil being equal to one thousandth of an inch.