What is the purpose of top side rails in a container?

The purpose of top side rails in a container is primarily to secure the roof panels to the container. These rails provide structural integrity to the container by helping to maintain the shape and stability of the roof, ensuring it remains robust during transport and handling. Additionally, the design of top side rails enables them to connect with the roof panels effectively, which is crucial for maintaining the waterproof characteristics and overall safety of the cargo housed within.

While options that discuss stacking, manual movement, or corner fittings might seem relevant, they do not accurately reflect the primary function of the top side rails, which focuses on the integrity and secure attachment of the roof panels.