The Fat Mouth is the secret behind Thule's universal mounting systems. The Fat Mouth can adjust to any size bar, be it Thule, Yakima, or a factory-installed rack. This one size fits all design also lends itself to moving rack hardware from one car to another, a super handy feature for families with a variety of outdoor interests. The Fat Mouth can be used with a wide variety of Thule rack hardware, including some bike mounts, ski mounts, and gearboxes.