The piston rod is a fundamental and critical component of every hydraulic or pneumatic cylinder. The piston rod typically is a precision machined length of hard chrome plated cold finished steel bar which transmits the force created by the piston to the machine component doing the work.
The pressurized oil moves the piston which then moves the rod. The counter movement is created when oil is driven to the other chamber and the piston moves back, pulling the rod. Two or more hydraulic cylinders can also be made to work together.