A crossbar system for a truck bed and methods of mounting a crossbar system to a truck bed are disclosed. In some examples, the crossbar system may include two towers, each coupling an end portion of a crossbar to a truck bed wall. Each tower may include a crossbar housing having a clamp device for securing the crossbar housing around a selected location along the crossbar, and a coupling mechanism configured to secure the crossbar housing to the truck bed. The crossbar housing may have a ledge portion configured to sit on an upper surface of the truck bed wall. The coupling mechanism may include a hook member configured to removably engage the ledge portion of the crossbar housing; and an over-center lever that is operable between open and closed positions, which may cause a bridge piece to move between unclamped and clamped positions. The coupling mechanism may include a plurality of alternate bridge pieces, each configured to engage a different truck bed rail structure.