[Jon McCarthy]

Kevin,

In my experience I reckon you have put your finger on the most likely
culprit, the plating of the wheel nuts.

Back in my "yoof" I raced an Austin Healey Sprite Mk2A as one of a team of
three from the MGCC Qld Centre. One of the cars had chromed wheels and nuts
which were for ever coming loose. The owner was very proud of its appearance
until he kept having the wheels flapping. Not something you want on a race
track. To say the scrutineers were unhappy was to put it mildly and he soon
changed the wheels & nuts.

I suspect that the thickness of plating is variable more on small
dimensioned items like nuts. These are very small relative to most things in
a plating tank.

Worth having a very close look and measurements taken maybe under the
microscope.

Regards

Jon McCarthy