Bottle tops?
Droopy, now you are just nitpicking.
The reason that your rotor head stays where it should is because of the friction provided between the threads of the "Jesus" nut and the main shaft. The torque is transmitted by the splines - but you knew that.
If, quote:- " screw threads are for bottle tops", try flying your helicopter without the "Jesus" nut.
Good luck!
P.S. The B747 trailing edge flap drives are of "bottle top" design - works well.