The U.S. aerospace/supplier industry decided in the 90's to be worldly and switch to metric. Upon realizing there were billions of engineering drawings, billions of MIL AN NAS specs/drawings, billions of tools, billions of measuring devices, millions to be trained, that tolerances and tolerance analysis had a "rounding" issue when converting, vendors would have to be revisited for compliant audits, and a billion other issues...the idea was summarily dropped. I believe Boeing, Airbus and others use the Imperial for most parts. The scientific community usually uses metric. The medical field uses metric. Doctors think you pronounce centimeter "sonometer", weird schools they go to. A sonometer measures plucking.
