“Mil” and “thou” are the same. They are imperial measurements both are synonyms for 0.001 inches. This unit is normally referred to as a “thou” (which is short for a thousandth), or (particularly in the United States) a mil. Mil has its origins from metric prefix “milli”, which is Latin for “one thousandths”. Plural of mil is mils and plural of thou is thou.
Alignment by Daus Studenberg CRL