Thanks all!
I'd normally use brass tube, but in this case I'm rebuilding for some one and the coupling is virtually welded onto the shaft, so I can't get the shaft out of the hull
I can just about get a Dremel alongside and grind a hole in the prop tube, but I won't be able to solder anything on unless I'm dead lucky.
So.... 6mm would be perfect thanks Wicker IF it can be clamped from both sides and I'll check with Chylde Hall as well.
Thanks again all.
Tony
PS Sorry Barrie, I've not found what you mean as yet.