Abstract: In a roof-shield support system employed in mines, at least two levelling rams each acting between a shield frame unit and an associated gap-seal plate, the latter being arranged so as to be slidable relative to the associated shield frame unit. Each levelling ram comprises a cylinder, piston and piston rod, is arranged so that the piston rod has a longitudinal bore which is open at the piston end of the piston rod, and an elongated rod which is sealed relative to the piston rod being disposed within said bore. The bore is in use in communication with a hydraulic fluid system of the ram and after levelling has occurred by actuation of the ram the pressurized hydraulic fluid admitted into the bore applies a force to the associated gap-seal plate so as to ensure its continuing tight engagement with the adjacent shield frame unit.