Nikon F3 and F3HP eyepiece thread sizes ?

Dear all,
Does anybody know the actual thread sizes for both the Nikon F3 ( standard viewfinder ) eyepiece and the Nikon F3HP ( high eyepoint ) viewfinder eyepiece please.
I believe the standard eyepiece is 18.8mm.

Many thanks everyone,
John S

See post #2 in the following thread of July 21, 2019:

https://www.photrio.com/forum/threads/eyepiece-accessories-thread-sizes.168812/

Thank you Ian !
That's exactly the information I needed - much appreciated.

Best wishes,
John S