I keep seeing mentions of old versions and new versions.

What's the difference?

Cheers.

ones a hoop and the newer ones are more tri angled shape and have some caster as well as adjusters to get the self centering to work.
wosher makes them

Older MK wishbones were made with round tube. The newer ones are made with oval tube. The Indy R wishbones are triangular in shape

Phil

Old style wishbone;





[Edited on 27-8-09 by Hellfire]

Any important reason for the change? I have the older ones.

The old style wishbones are "a tad flexible", that is, they move around a LOT which leads to less caster under braking. I'm curently contemplating upgrading mine.