Normal people:
thread pitches should be nice round numbers and ideally common with other existing threads to simplify tooling
Here is my horrible child, 3/8 Inch British Standard Pipe Taper. He has 19 threads per inch, more or less, because no one will ever bother to actually make tooling for this deranged number and will just pick something close and vaguely easier to make. He is tapered, and seals when he is sufficiently turned. Which is hopefully before the minor thread pitch mismatch seizes the whole affair up. No part of this fellow is actually 3/8", by the by, that's just a sort of hopeful moniker we gave him. For some reason unknown to British ingenuity, these seem to mostly also have a o-ring seal in real life. ta-ta!
do the rest of y'all know how annoying it is to find a proper bsp threadmill that u can just... buy normally?
"oh look at me I use a 55° thread angle just to be special"
"u thought u were gonna get away with that one single form threadmill for most of your thread cutting huh well YOU THOUGHT WRONG"