You want us to throw away all our tools overnight? Recalculate every recipe, re-tool every process (with concomitant errors), etc, etc, etc, overnight

To the best of my knowledge, everywhere that has converted so far has just started making new things in metric. Yes, that leaves a weird state where you may see signs in one or the other, for example, but over time it resolves. Tools in other sizes would continue to be made as long as they needed to in order to maintain the old stuff until that gets replaced.