Hi again,
@pilot2
I finally remembered that I had bought a set of P3 Pro ND filters quite a few years ago - but because I have a such LOAD of drone stuff of all sorts, I had to track down where they were. I don't fly my P3Pro so much now because I usually fly my Mini2. My P3Pro was bought in 2016.
Anyway, I found the filters and have measured the internal threads of each of the 4 filters and they were all around 29.65mm, which, as the thread depth is quite shallow, I would suggests points more to 30mm. It may not help much but I've attached some photos of them - They are just cheap, generic lenses but they worked OK. I also have a lens which was sold as an 'Orsda' variable 'Fader ND2 to ND 400' but which I suspect that is merely 2 rotatable polarised lenses put together. Pics also attached... The reference codes didn't bring much up for me on the internet and the listed website seems dead now.
Hope this helps you in some way.
Steve