A bolster is a supportive structure or framework used to secure cargo or containers to their transport unit. In U.S. intermodal shipping, it refers to two main components:
Container Bolster
These are the specialized steel end-frames that, when connected by a floor, form a Flat Rack container. These frames are foldable and act as the primary lashing points for securing heavy and oversized cargo that is too wide or too tall for standard containers.
Chassis/Rail Bolster
This is the heavy steel beam structure found on a container chassis or railcar. It provides the necessary support for the container’s weight and contains the twist locks — the critical locking mechanisms that secure the container’s corner castings to the chassis, preventing the container from detaching during movement.