In a double-rod end cylinder, the piston surface areas are always:

In a double-rod end cylinder, the design inherently includes two identical piston surfaces at both ends of the cylinder. This equal surface area is crucial for ensuring balanced forces during operation and maintaining predictable performance. When both sides of the cylinder have equal piston areas, it allows for consistent movement and response to hydraulic or pneumatic pressures applied to either side.

This balance also means that the forces exerted by the fluid pressure on each side of the piston can effectively counteract one another, ultimately resulting in stable operation across the stroke of the piston. An unbalanced surface area would lead to unequal forces, complicating the operation and potentially causing issues like unintended movement, wear, or failure of the cylinder.

The other choices do not accurately reflect the characteristics of a double-rod end cylinder. The idea that the surface areas are greater than fluid pressure or less than the rod diameter does not pertain to the fundamental design of the cylinder. Additionally, the stroke primarily refers to the length of travel of the piston and does not dictate surface area dimensions, further confirming the correctness of equal areas in this design.