I think they are M38.
I have a pair in my workshop, so if there are any measurements you want me to take just let me know and I will get them tonight for you

 

The outer diameter is 40mm, the inner diameter is 38mm, thread pitch is 1.5mm

 

Thanks for that, but only just seen you reply. Can you buy the balljoint holders?

Cheers

Paul

 

I had mine made up.
An old friend made the cups years ago and Billingham Machine Co tapped them for me..
It was costly as they had to buy the tap.
Or so they said.

 

Pretty simple job to cut an internal thread on a lathe, more sp once you've done one