I've spent maybe 10 years in US units, 10 in metric, and 10ish in Chinese units (16 was involved but not any more). (I think I'm still 20ish:)
Having a unified uint system around the globe is a definitely good thing. From my experience, metric units are easier, better learning curve, and more understanding, less memorizing, less proud for Americans, but ok. Yeah, screw sizes and drill bits are a mess in US, compared with those used in metric countries. I have a 35-year old steel ruler from UK that has decimal inches on it. Guess that was what went around UK in the 70's, hoho. Decimal is just more natural with our 10 fingers (how do you count 12 with hands as kids?). You spend more time using the units than just plain memorizing weird numbers.
Maybe there is a reason to keep using difficult units so that everyday joes won't want to understand stuff like science/engineering and just be skilled workers with not much thinking and be happy with what's given to them (my conspiracy theory again).
Having taught college physics for the past 10ish years, I really hate how much the US has embraced with metric units at high school level and elsewhere. I've done enough designs (metals, PCBs) with inches and every time I struggled through. I like decimal inches better than fractions but fractions do look neat and "professional"(?!).
Think about the Lockhead tards and what they did to crash a multi-billion Mars explorer. We're better off using a single unit system.
Well, back to suggestions. I would use mm and have approximate inches in parentheses like 25mm (1inch), use numbers that are maybe close to nice inch numbers and fractions so your US readers have a grasp of reality.