WOW, what a disaster. I just assumed it would be US. My brother bought a P-51 last week and so you get to thinking about support equipment and special tools you might need and that's why I had to ask. I'm into threads/taps/dies and threading on my lathe. And I've had to tackle the metric system on a few occasions and won but at age 65 I don't know if I'm man enough to take on another threading system. I hope we never have an engine problem. The Merlin is already unbelievably complex compared to the auto engines I'm used to without having to think about threads. Thank you for the information.