On 06/08/2020 13:45, jon wrote:

How difficult do you think it would be to get an adapter ring 0.25" width,
with 25mm x32 internal thread and 28mm x32 external thread. Well it is
nigh on impossible, although the threads are standard in photographic
equipment. All other combinations of adapter rings with these external/
internal threads are readily available. I am not going to buy a lathe to
make my own, I only need one.

Unless size is critical can you achieve this thread combination by using
2 or 3 available adaptor rings together