As I understand it:
39mm is 0.5mm pitch from Leica, Hoya, B+W and everyone else.
46mm is 0.75mm pitch from Leica, Hoya, B+W and everyone else.
So for these sizes and several others (including, as far as I can tell, 34mm/0.5mm), thread pitch simply isn't an issue. I think there are some incompatibilities for filter diameters between 39mm and 46mm, including 43mm and 40.5mm. Leica apparently used a 0.5mm pitch in the earlier E43 Summilux, but 0.75mm is otherwise commoner. B+W at one time made both 0.5mm and 0.75mm versions of their 43mm filters. Hoya apparently only makes 0.75mm, and yet I've tried two of them and they both screw on my E43 Summilux all the way without binding or damage. Make of that what you will!