[rootusrootus]

> only for the reason that everyone else is using it

That is an honest answer, which is refreshing. Beside that, there is not really any particular reason that the US has to make SI mandatory. We adopted SI nearly 50 years ago, we just did not make it mandatory. The US has a bit of national identity which leans towards rebelling, so making SI mandatory would probably be contentions anyway. And it's just not worth the argument, since it buys us very little of actual value.

[runarberg]

Temperature is easy, probably the easiest unit to convert... Everyone would get used to it pretty soon after they started using it regularly. There would be some legacy systems out there which would annoying to convert (which is already the case) but within a generation nobody would bother with Fahrenheit at all.

I think the hardest unit to convert is probably length as there is not only a bunch of legacy systems and equipment out there, but Americans are very accustomed to fractional sub-units as opposed to the decimal cm, mm, etc. I’m not sure e.g. the building industry would ever stop saying e.g. four and five eighths. Personally I hate fractional lengths when using american tools. E.g. I’m used to a 11 mm wrench being smaller than a 13 mm wrench. I need to stop and think before I know which is smaller a five eights or a three quarters.

[rootusrootus]

> american tools

That's an interesting way to phrase it. I, and everyone I know, have both metric and SAE tools. At least for wrenches & sockets.

> I need to stop and think before I know which is smaller a five eights or a three quarters.

I'm with you there. I've gotten in the habit of just mentally converting every SAE size to 32nds. I wouldn't really mind losing SAE, but that is not happening. What really makes my blood pressure goes up is Ford ... they mix metric and SAE fasteners on their cars. WTF! Pick one! Subaru is at the other end, easy to work on because 10 & 12mm wrenches will work for maybe 9 out of 10 bolts or nuts.