We only get down to proper metric units when dealing with the fiber itself, but even that is lashed to aerial pole-to-pole strands, where the steel strand is in US units, all of the hardware is US.
The battery backup shelves for large AGM lead acid batteries: All US units. The batteries themselves are specified in inches and pounds. Once again it can all be converted, but that's the default unit from the manufacturer. Floor loading calculations? Pounds per square foot.
https://en.wikipedia.org/wiki/Mars_Climate_Orbiter
>However, on September 23, 1999, communication with the spacecraft was lost as the spacecraft went into orbital insertion, due to ground-based computer software which produced output in non-SI units of pound (force)-seconds (lbf·s) instead of the SI units of newton-seconds (N·s) specified in the contract between NASA and Lockheed.
American in a highly technical field here. I have no issues with using SI units when appropriate. But there is a tremendous lock-in, at least in some areas. Aerospace is a nasty mishmash, resulting in things like aircraft that "think" about altitude in feet, fuel in pounds, gear displacement in inches, but electric field strengths in W/m^2 and geopositioning in meters. All of those choices were made long ago, I'm stuck with them. My only defenses are to keep meticulous track of units and convert where necessary (while paying attention to things like numerical error).