These roof racks are made from aircraft-grade aluminium offering a sturdy construction. The T-slot design allows easy installation with high strength and low air resistance. Please choose carefully the correct size as each option has a maximum fitting width (the distance between your rails). How to choose the right size? Measure the distance between your rails (from outside) Choose Size 1 if the external distance between your rails is equal or less than 1080 mm Choose Size 2 if the external distance between your rails is equal or less than 1230mm NOTES: If your rails are not parallel and have different distances at the back and at the front, please choose the largest suitable size. The clamps are adjustable for a better fit. You need to have raised roof rails (sidebars) installed on your car in order to install this item. Minimum 30mm gap between the roof and roof rails are required. These roof racks are suitable for raised roof rails with a gap between rail and roof. It is not suitable for solid roof rails (flush) without a gap. Please provide a physical address at checkout.