There is still plenty of scope for tears. I had a Shimano internal hub gearing system on a bike. It had a bolt and nut with a thread that was unusually tight. More threads per mm.
It was very easy to strip and I did it numerous times. Every second time I ordered new ones the wrong ones came and I’d strip them too.
Internal hub gearing is amazing, but comes with intense pain.
The metric standard distinguishes 3 thread pitches: regular, fine, and superfine. So even if you say it's the same standard, not everything of the same size matches.
I also have Shimano internal hub. It's claimed spare parts are impossible to get. Of course just a screw might be different. When it broke it was replaced as a whole, luckily on warranty.
Basically 2: metric and imperial. It's quite common for shops to have both.