Sounds like 1" dairy tube. Dairy tube is measured by od so 1" tube is about 7/8" id. Also sounds like you have a ferrule on the end of the tube. If you can get a 1" dairy tube cap you can drill or plasma cut a hole large enough for a 1/2" coupling to pass though and weld it to the cap. That would give you a thread for your dip tube and a thread for your ball valve.