Thule is a popular brand of car-mounted carriers and cargo boxes that can store luggage, bikes, skis and other belongings.
Although many accessories are available through Thule, the basis structure of a Thule system is comprised of long parallel bars that stretch across the roof the car. The system contains feet that are sold specific to each brand of car. The feet attach the bar to the car. You might adjust the feet if you're changing the Thule accessory--for example, if you're changing from a bike rack to a ski rack.
Unlock the tensioning lever if your rack is equipped with the optional lock. Do this with all the feet that you will adjust. If your rack does not have a lock, skip this step.
Decide which bar you want to work on first. If you want to work on multiple bars, you should adjust the feet on only one at a time, so the other bar remains as a reference point and so that the Thule assembly doesn't fall off your car or dent your vehicle.
Lift the tensioning lever on both sides of the bar that you will work on first. This releases the tension that both holds the foot to the top of the car as well as holds the Thule bar to the foot. This will enable the bar and the feet to move.
Slide each foot forward or backward as needed, based on your adjustment preferences. Slide with your fingers, manually. To ensure that the bar is perpendicular to the car (as it should be), you can measure the bar against the corner of the windshield on both sides of the car to make sure the two measurements match.
Re-tighten the tensioning lever by pressing downward with your hand on the lever. This will lock it in place.
Repeat steps 2 through 5 with the other bar, if you want to adjust the feet on both bars.
Some Thule accessories such as roof boxes have a specified acceptable distance between bars. In this case, you can measure the distance between the two mounting points on the Thule accessory.