A threaded rod can be pivotably coupled to the tonneau cover via a proximal end. A housing can have first and second housing portions slidably coupled to the threaded rod and moveable along the threaded rod relative to each other between locked and unlocked positions. The second housing portion can include a channel positioned to receive a downwardly disposed distal edge of an inboard flange. Locking pawls within the housing can move to engage threads of the rod to prevent movement of the channel relative to the elongate member when in the locked position. The locking pawls can move to release the threads of the rod to allow movement of the channel relative to the rod when in the unlocked position. A biasing member can apply a biasing force biasing the housing toward the proximal end of the elongate member and biasing the housing toward the locked position.