What gas cap will fit on my 65 Valiant?

i had the same problem i couldnt find any where that made a cap that worked so i went to pep boys found the closest locking key cap that almost fit went in the parking lot got a flat head and hammer then where the fuel tank tunnel hole a little bigger no leaks or nothing cost me $12.00 i like the key locking one so no one can pee in my tank ahahah