The original front bolts for the lower ball joints have a disproportional oversize head.

I never even thought much about it but it makes sense now.

They are wheel stops!

They prevent the spindle from hitting the control arm during a very sharp turn.

They are missing in the white car but I know they are still on Mark's convertible.

For the 2+2, my upper ball joints were a different brand but the bottoms are Moog.

The replacement joints just use regular nots and bolts.

If you car still has them, you may want to keep them.

If your wheel is rubbing during a sharp turn, you may want to check for these on your car 

Yes, you want to keep the original stops when doing the lowers. Good advice to prevent rubbing.

I just got my uppers and lowers today. Delphi, made (assembled) in Turkey (sorry, my bad, Turkiye) of all places, and they have the stop bolt.

Imagine that!

Interesting.   I've noticed these round head bolts facing forwards on lower ball joints on cars I've taken apart, I really wasn't sure what was up with them.   I think the ones in my photo came with the last set of Moog lower ball joints I put in my 2+2 convertible in 2018, but not sure.  They certainly are new not used.