Lock cylinders can be purchased in multi-packs or as individual cores to secure roof bars to the vehicle. They do not come pre-installed in the crossbars.
The Thule OneKey system allows the cylinders to be matched with other Thule carriers and racks. To order matching locks, enter the "N###" code printed on the lock to the Keys and Locks page:
https://www.thule.com/en-us/us/thule-support/spare-parts-keys