Securing of container during transport

The mechanism for locking and unlocking bolts (21) for fixing a freight container in position comprises a hydraulic unit with a piston rod (40) which carries an outer (60) tube. Each of these carries a cam (52, 61). The cam (61) on the outer tube can be moved from an upper to a lower position. Independent claims are included for: (a) a system for selectively adjusting the position of a mechanism, as described above; and (a) a method for locking and unlocking bolts for fixing a freight container in position using the mechanism.