These are problems you actually pretty much never have in actual precision manufacturing in metric... Most general machining is done to a tolerance of +/- 0.1 -

These are problems you actually pretty much never have in actual precision manufacturing in metric... Most general machining is done to a tolerance of +/- 0.1 - what does half a millimetre have to do with anything? As for building, that's mostly just rounded to the millimetre, centimetres aren't usually ever used.