I am in the metric system well nearly! In the UK we have a mishmash of metric and American imperial (UNC UNF NPT etc.) and British imperial. We have metric and imperial tube sizes but still use imperial pipe sizes and threads (BSP BSPT) then some old stuff is the old (BSW and BSF)
In my opinion (for what it’s worth) the old BSW/BSF threads are by far the best just wish the metric system used the thread form (55 degree rather than 60 degree) Mr Whitworth certainly got this right. However, the metric thread system is so easy to understand: simply take the pitch away from the outer diameter and that gives you the core size or if you like the drill size. This almost works for any metric thread (M8 x 1.25mm is an odd ball, A 6.8mm drill is recommended as a 6.75 drill is non-standard)
So not sure if we will ever have a full metric system
The Home Engineer