I've seen the KOP. Gorgeous pen. Even better in person.
On my pen I used M12x.75 (34 tpi) for section to body threading. I've just ordered an M11x.75 for the next smaller size.
The cap to threads are 5/8"x28 tpi. I got the tap and die from... ebay? Victor? I can't remember. They're easily available sizes though.