Are you talking about the hitch itself?
If so, go with a Class III from either Ford, Curt, and any other brands. Hitches are vehicle specific. If it doesn't say it is for a Sport Trac, odds are...it wont fit and if it does fit, it is going to look stupid.
Do not go with UHaul. They will not rent trailers to Explorer owners. The way I look at it is this. If they don't want to rent to me because of my vehicle, I won't give them any of my money.
If you are looking for an insert, there are only two sizes. 1" and 2". If it looks small, it is a 1". If it looks normal, it is a 2".
Personally I see no point in buying a Class 1 hitch.
Tom