Does anyone know what thread the rear strut tube/Insert retaining nut have? My measurements indicate 1.885" over the nut male thread with a tpi around 23. This would equate to American 8-Thread series (but that is unusual). I would have thought the British Brass thread at 26tpi would have been likely although the British Cycle thread would seem a better contender at 24tpi for the 1 5/8" dia - I cannot find data above this dia.
I can confirm that the thread is 1.885" dia x 24 TPI. I have had a 5 minute look through my engineers handbook and failed to identify it.
With such an odd dimension, I guess it is a special designed for the application.
You don’t say why you want to know what thread it is.
If for some reason you have to repair the thread in the tube, you will need to speak to Tony Thompson as he has a tap specifically designed for such a purpose.