Hi Andrew,
Portavadie was awsome, but I was only there a night on my way to Ardrishaig for the Crinan Canal. Teal is kept at Kirkcudbright on the Solway, so not too far to go to the West Coast. Look me up if you come in there on your way south. (0759 257 4415)
I did go to the Chandler's today and found a Plastimo "anode conical nut" Zinc Ref: 38248 This is the 30mm greatest inside diameter size and was a bit loose, but by screwing the bolt tight, it fitted well and externally was flush with the shaft. I think the correct size (partly on the advise of Peter Parker) is probably 22-25mm Part Ref 38247 but the chandler did not have one and I am happy to stay with what I've got.
Many thanks for your advice.
Bob Simpson
Teal 285/74