j_radcliffe said:If your radiator is vertical flow, then it is a 5/16th UNF inch x 3/4 inch long.
If it is a horizontal flow radiator then it is most likely a 5/16 in UNF x 5/8th inch long.
The other option I have listed is 'special bolt' with a 'spire nut,' with no size given.
James.