This leaves the carpenters/and builders. They have a minor concern but if the plans were in centimeters and tape measures were metric, they would be fine with it.
Dave
Having gone from carpentry/cabinetmaker to machinist to yacht designer, I'll take metric any day, as long as the switch is complete. Example: A manufacturer of RTA (ready to assemble) cabinets went from imperial to metric in their plant; errors dropped about 60-some per cent in the space of about 60 days. I made the switch as a machinist in about three days, using a $10 calculator. I saw the same thing occur in boatbuilding, where we went from imperial to metric during my stint. Everyone whined until they got a set of metric plans and new measuring tapes. Errors down, productivity up. No more feet, inches, eighths, sixteenths, thirty-seconds, big lines on the tape, little lines, itty-bitty lines. The hangup, in my mind, is big industry and American Chauvinism. And still big industry whines about having to compete against the world, but won't grant themselves the advantage of competing equally.