I have a 2000. I just went out and put a 1/2 inch flare nut wrench on mine...13mm open end is half a hair loose. Ford transitioned to Metric (sort of) as model years progressed, so I'd try both a 1/2 and 13mm on yours for sizing purposes before purchasing a flare nut wrench. Note when you check the sizing that you will need a flare nut wrench with sufficient angle at the business end to allow the wrench shank to clear the valve cover. Hope this helps.