These racks work on Thule racks that have a groove in the center of them. The square bolts on the bottom slide into the center of the rack.
I got the following from AI...
You need aero-style crossbars with a T-track (T-slot) channel on top. Thule says it installs directly into the WingBar Evo or AeroBlade T-track. Compatible Thule bars include:
WingBar Evo, WingBar and WingBar Edge
ProBar Evo
SlideBar
AeroBlade
Xsporter Pro and TracRac (truck/van)
That list comes from Roof Racks UK and Amazon's listing. For a new setup, the WingBar Evo is the most common choice.