Paul, you are correct about the pin, it’s use is only for pivoting the mast when raising or lowering. When sailing there should not be any pressure on the pin and it should rotate freely.
The class rules state a pivot pin diameter 6mm (1/4″), there’s an example on Trident’s shop;
http://shop.trident-uk.com/acatalog/Other_Spar_Fittings8.html
You certainly want to use plain rod rather than a bolt, I would guess it’s pretty easy to make one yourself if you have access to suitable materials and tools.
bob
PS
If anyone knows where you can get mini R clips rather than split rings/pins perhaps they could let us know.