[Healeys] Radiator cap

[Pieter and Linda]

thank you all for the advice and suggestions. I have 2 caps here that are the
correct part number according to their respective manufacturers websites ( CPC
and Tridon) yet they both JUST reach the bottom of the filler neck and turn
without any downwards pressure from me. Since I don't have a Healey specialist
nearby, can anybody tell me if the rad cap also fits a more common vehicle so
I can try and ask for it at the local parts store?
cheers