The Cross Clamps mount to your seat tube to make your top-routed cables compatible with bottom-pull road derailleurs.
Whaa? Well, you wanna race 'cross, right? But 'cross frames have top-routed cables, requiring a top-pull front derailleur. All the good, light components tend to be coopted from road groups, which have bottom-pull-only derailleurs. Lots of 'cross frames have a mount for a pully already integrated--the Cross Clamp allows you to do this with any frame. Get it?
Three Cross Clamp sizes to accommodate common seat tube diameters
Cable Pulleys repace worn Cross Clamp pulleys, or mount directly on pulley-ready frames