Clamp for a cross bar

A clamp (14) for use with a cross bar (12) of an existing vehicle article carrier to allow accessory vehicle article carrier components to be secured to the cross bar (12). The clamp (14) includes a base portion (16) and a clamp element (14) hingedly coupled to the base portion (16). A locking assembly (42) allows the clamp element (14) to be secured to the base portion (16) without any external tools. The locking assembly (42) includes an over-center locking lever (54) which can be pretightened before being moved from an unlatched into a latched position to thus allow a pre-tightening force to be applied to the clamp element (14). The clamp element (14) also includes a C-shaped channel for receiving a tap plate (39) or other similar component associated with an accessory article carrier component.