What the Different Parts of a Shipping Container Do
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A shipping container looks like a simple steel box, but its strength comes from a set of parts that each do a specific job. Knowing what they are, and what they do, makes it much easier to understand why containers are so robust and to describe any wear when you are buying a used unit.
This guide walks through the main parts of a shipping container, working from the corners inwards.
The Frame: Corner Castings and Posts
The structural heart of a container is its frame.
- Corner castings are the heavy steel blocks at each of the eight corners. Every lifting, stacking and securing operation happens through these, as cranes, twist locks and lashing gear all connect here. They are the single most important structural fitting on the container.
- Corner posts are the vertical steel columns that join the top and bottom castings at each corner. They carry the weight of every container stacked above, which is how units can be stacked several high.
- Top and bottom side rails run the length of the container along the top and bottom edges, tying the frame together and supporting the walls and roof.
The Understructure: Cross Members and Floor
Beneath the floor sits the understructure that carries the load.
- Cross members are the steel beams that run across the width of the container underneath, spanning between the bottom side rails. They support the floor and spread the weight of the cargo.
- The floor is usually made of heavy duty marine plywood laid over the cross members, chosen because it is strong, hard wearing and able to take the weight of a forklift.
- Forklift pockets are fitted to many 20ft containers, allowing the empty unit to be lifted and moved by forklift.
The Shell: Walls, Roof and End
The outer shell keeps the weather out and adds rigidity.
- The side walls and roof are made from corrugated weathering steel. The corrugations are not just for looks: those ridges make thin steel panels far stronger and stiffer than a flat sheet would be.
- The front end wall, opposite the doors, is a fixed corrugated panel that braces the container and helps it keep its shape.
The Doors and Their Fittings
The door end is where most of the moving parts are.
- Cargo doors: most containers have a pair of steel doors at one end, giving full width access.
- Locking bars, also called lock rods, are the vertical steel bars that run down the doors. Turning their handles rotates cams into keepers at the top and bottom, holding the doors firmly shut.
- Cam keepers are the fixed brackets the cams rotate into, at the top and bottom of the door opening.
- Hinges allow the doors to swing open, usually to a full 270 degrees so they lie back against the side walls.
- Door gaskets are the rubber seals around the door edges. They press together when the doors close to keep wind and water out, which is what makes a sound container weathertight.
- The door header and sill are the horizontal steel members above and below the door opening, framing it and adding strength.
Why the Parts Matter When Buying
When you inspect a used container, most of the things worth checking relate to these parts: sound corner castings, a solid floor, straight doors and, above all, gaskets that seal properly. Because we hold our own stock, we can send you photographs of the actual container before you buy, so you can see the real condition of the doors, floor and shell rather than relying on a generic image.
We supply containers across Sunderland, the North East, Teesside, Scotland and the Borders. For more on sizes, see our complete guide to shipping container dimensions, or get in touch if you would like help choosing a unit.
Frequently Asked Questions
What are the main parts of a shipping container?
The main parts are the corner castings and corner posts that form the frame, the cross members and marine plywood floor beneath, the corrugated steel side walls, roof and end wall, and the door assembly with its locking bars, hinges and rubber gaskets.
What are corner castings on a shipping container?
Corner castings are the heavy steel blocks at each of the container’s eight corners. They are the points through which the container is lifted by crane, stacked using twist locks, and secured for transport, which makes them the most important structural fittings.
What is the floor of a shipping container made of?
Most shipping container floors are made from heavy duty marine plywood laid over steel cross members. Marine ply is chosen because it is strong, hard wearing and able to support the weight of a forklift moving inside the container.
What keeps a shipping container watertight?
The rubber door gaskets are the main seal. When the doors close, the gaskets press together to keep wind and water out. Sound gaskets, along with an undamaged corrugated shell and roof, are what keep a container weathertight.
What are the locking bars on a container for?
The locking bars, or lock rods, are the vertical steel bars on the doors. Turning their handles rotates cams into keepers at the top and bottom of the door opening, holding the doors closed and helping to compress the gaskets for a weathertight seal.