I had the same question and actually phoned Happ a few weeks back about it...
The answer I was given was that the 3" high-
lip trackball should fit in any of the 3" kits that they have,
except for the kit made for the
high-ball. While on the phone I asked about the parts on the following page, and was told that either "55-1101-00", "55-1102-00", or "55-0321-00" (the one you're referring to) would fit a 3" or 3" high-
lip trackball:
http://www.happ.com/trackballs/55110100.htmAccording to the guy I spoke with on the phone, the "high-
ball" mounts the ball higher and so it requires a wider hole to put the ball through. As for all of the other 3" kits, he said that they'll all fit a 3" high-
lip ball.
I hope he's right too... I'm about to order the "55-1102-00" mounting kit myself...
Can anyone else confirm this as being correct or just crap?