These towers do just what the name suggests, grab on to your factory rails. I added them to a Subaru Outback. Installation was straight forward, with the required Allen wrench included. To install, there first is a height adjustment, then a bolt to tighten to grab the rail, and another bolt to tighten to clamp down on the bar. End caps are included, so no need to buy extras. Pick up a round bar and some locking cores, and the system is ready for a rack.