Tie-rod air cylinders have blocks capping each end that join by threaded tie rods to keep them securely in place. Double-acting tie-rod air cylinders interact with pressurized air to both extend and retract the actuator rod, allowing for motion control in both directions. Single-acting tie-rod air cylinders only convert air pressure to motion in one direction, then return to their natural position at rest. Mounting hardware for tie-rod air cylinders enhance the mounting possibilities and expand use of air cylinders. Replacement parts for tie-rod air cylinders replace worn or damaged components in compatible actuators.