[Healeys] Starter solenoid

[P.J.Aeckerlin]

Friends,
I intend to put a surplus Lucas starter solenoid 76471H up for sale but 
unfortunately three out of the four nuts are missing.  In my 40 years or 
so of fiddling with motorbikes and cars I have built up a nice 
collection of funny nuts, but none of these fits. The thread on the 
(copper) studs has a diameter of 0.3" and the thread has, according to 
my thread gauge, 19 threads per inch. Not that I have such a gauge, but 
18 tpi is too coarse and 20 tpi is too fine.
Anyone has any idea what thread this might be or, even better, anyone 
able to sell me three nuts?
Thanks in advance
Jack Aeckerlin, The Netherlands
1964 BJ8 29432