sam is correct. The PRO 60 and PRO 80 share the same components in the driver with the 60 being a smaller cone. And also a bit smaller housing. But, the costs are the same in the manufacturing so the only place to take some out to be able to offer the 60 at a lower price is the clamp. Or they would be the same price.
The 60 clamp comes with rubber caps that protect the tower. This clamp comes with the MB-8 as well. You can also upgrade the 60 or MB-8 to the Trick Connect 2 clamp. The TC2 clamp adds the rubber inserts, quick disconnect and built in swivel. I plan on adding more detail on our site with this info. But you can order the TC2 clamps on their own to upgrade older speakers, or you can order a new set from the start with the TC2 clamp.