One advantage of a smaller pitch is that it allows more wall thickness when using the same diameter threads. E.g. a 14x0.8 cap thread with 12x0.75 section threads inside of it will allow more wall thickness than a 14x1 with the same 12x0.75 threads inside.Most all of the pen kits (the majority of them) are closer to 1.0 than 0.8 in pitch.
For something this size, M14, 1.0 to 1.25 should be in order.
I have a Noodler's Ahab pen with that threading setup (14mm w/ 12mm inside - eyeball measurements). Comparing the cap threads with one of my pens with 12x0.8 cap threads shows the the same thread spacing - it's definitely not more than 0.8 pitch (again, eyeballing). FWIW, the Ahab cap threads are double-start.