Like squeeze said, the fork should snap on to the ball. I know there are different lengths, but also not sure about larger balls.

The tip of the fork is all that grabs the throw out. You also have to have the clips of the fork inside the bearing. Looks like this when put tigether...

http://img.photobucket.com/albums/v228/Avette4me/Vette/Tremec/install/08.jpg