what ball joint do i get for my explorer?

call the dealer, They will be able to tell you what ones you need, As for buying them, I would buy the ones with the best warranty. I put a set on my Blazer, they were 1/3 more than the "cheap" ones and they have a lifetime warranty... Once you find out from the dealer which ones you need (while you are taking to them, ask them how much and what there warranty is), go to a auto part store and ask at the parts counter, they will have a choice of them. But dont forget about the warranty and dont just pick up the cheapest ones or you will be doing this all over again in a year or two. best of luck