Attaching system for a vehicle roof box to a frame

The fastening, which is one of a number holding the base of a luggage box on the vehicle roof, comprises a body (1) with a pair of clamping hooks (6) to engage with a transverse bar when actuated by a drive. The upper ends (7) of the hooks are pivoted to the actuator (10), which has a threaded outer surface (11) that engages with the inner surface of a locking cap (15). When the cap is rotated in one direction the hooks are opened, while in the opposite direction they are closed to grip the transverse bar.