If you only need two towers e.g. you're outfitting a truck cab with a rooftop car rack system this is the option for you. The Q in Q TOWERS stands for Quadruple Movement. That means the tower and clip move in four different ways, so they'll fit your vehicle like a custom tailored tuxedo. The Yakima Q Towers 1Pair allow you to set up your gear without having to buy two extra towers. Die cast interior for solid, sturdy anchor Each tower's ball and socket mechanism adjusts to all contours of your vehicle Add vehicle specific Q Clips 00601 00730 to ensure a custom fit to your doorframe Upgraded for easier and faster rooftop car rack system installation SKS lock core compatible sold separately Updated crossbar tightening system, one time measuring for a precise fit Also sold in sets of 4 for full rack systems.