I think there might be a question as to the definition of things here:
Trailer Hitch - The mount that bolts to the truck and is semi-permanently mounted. These are rated for different classes, I,II,III,IV,V.
Ball mount - The square piece that attaches IN the trailer hitch, comes in the same classes above. The ball bolts in one side, the other slides into the hitch.
Ball - Comes in different sizes this bolts to the ball mount, and the trailer locks onto it.
I believe the OP is asking which hitch will fit his frame on his truck. It seems according to the Hitch Store (website) it depends if your truck was built before or after November 2002. If after, it is the same as 2003-2008, if it is before, it is different.
Source:
The Hitch Store, Trailer Hitches Online
