UCA ball joint interchange?

I know they are "bigger" my question is, is the diameter of the ball joint where it screws into the control larger or is it the tapered shaft the goes into the steering knuckle larger? I ask be cause the car I have already had a disc brake conversion and I'm not sure what I have.
I ordered bushings so I can use the small ball joint in the bigger spindle as well as the small and big ball joint to on use dependingwhich control arms are on the car now