I presume this is standard fare for Yakima. As my first exposure to the design, I find it clever and effective. Basically, the facing plate (pictured here the trapezoidal part with "YAKIMA" imprint) is a lever, that when pulled out, withdraws two locking bars (seen here as little step protrusions on either side of the bottom part), and conversely, when mounted on the car, the lever turned up and home (and locked, if you opted to purchase that option), the locking barrels rotate outward to lock solidly in the feet (Yakima calls "landing pad"). Really nice touch is that Yakima included a 3.5 Nm torque tool for torquing the screws and bolts. One minus for the locks -- they don't retain well, and want to come out when unlocking, and in practice, one has to develop a habit of holding the lock in with one hand while withdrawing the key with the other.
2011 BMW 3 Series 4dr