Abstract: Disclosed herein is a hydraulic jack comprising a cylinder and a piston rod assembly which is movable between a retracted position and an extended position relative to the cylinder. The jack also has mechanical locking means including a rotatable shaft and movable into engagement with the piston rod assembly in response to rotation of the shaft, thereby to lock the piston rod assembly in its extended position. The locking means reinforces the piston rod assembly in its extended position along substantially the entire length of the piston rod assembly.