i just tried to pull the lower connector out of the radiator good luck i had 2 bad radiators in my shop and both i couldn't get out id ether use a compression fiting on it or a good set of hose clamps. i went out to look since know one else new what your trying to do. looks like 5/16 or maybe 3/8 line note mine were factory radiators no nut just the barb fiting sticking out