"Hence it was determined that the unit of length taken should be the ‘mil,’ and that the decimal system should be adopted for expressing dimensions." 'mil' above meaning "thousands of an inch" - hence the use of "thou" and fractions thereof is banned since August 1882. 1st Report: https://www.sizes.com/library/technology/thread_BA1.htm 2nd Report: https://www.sizes.com/library/technology/thread_BA2.htm