Freight reference · interactive
Twistlocks, fittings and lashing
What holds a container to the ship, the truck and the train, and what holds the cargo inside it. Hover over the diagrams, or tap them, to see each part explained.
نسخه فارسی: توییستلاک، اتصالات کانتینر و لشینگ
Corner castings and twistlocks
Containers are joined only at their corners. Each of the eight corner castings is a hollow steel block with standard holes, and a twistlock is the small lock that connects two castings: its cones go into the oval holes and turn a quarter turn to lock.
Hover over a part for a moment, or tap it.
Corner castings and the twistlock
Every container has eight corner castings. A twistlock joins the bottom casting of one container to the top casting of the one below. Hover over a part, or tap it.
Types of twistlocks and fittings
Different locks are used on ships, in holds, on trucks and on trains. The ones you will meet most:
Manual twistlock
Inserted and turned by hand with a handle. Cheap and simple; common on older ships, barges and in depots.
Semi-automatic twistlock (SATL)
Fitted to the bottom corners on the quay before the box is lifted aboard. It locks itself when the container is set down, and is opened with a pole that pulls its release wire.
Fully automatic twistlock (FATL)
Locks when set down and releases when the crane lifts the container straight up with a slight tilt. No lashing crew needed between tiers, which speeds up port work on large ships.
Base twistlock and foundation
Locks into fixed sockets welded to the deck or hatch cover, often dovetail foundations into which the lock slides.
Stacking cone
Locates containers in the hold without locking them. Single and double cones exist; double cones join two 20 ft boxes side by side.
Midlock
A lock for the middle of a 40 ft cell when two 20 ft containers are stowed end to end in it.
Bridge fitting and lashing gear
Bridge fittings join the tops of neighbouring stacks. Lashing rods with turnbuckles secure the lower tiers on deck.
Chassis and wagon locks
Trucks and container wagons have their own twistlocks or fixed spigots at the corners. All four must be engaged and locked before the vehicle moves; an unlocked box can fall off on a bend or when braking.
Lashing containers on a ship
Below deck, the hold's cell guides hold containers in place. On deck, twistlocks join the tiers and lashing rods tie the lower tiers to the ship. The ship's crew or the terminal's lashing gang does this work following the ship's Cargo Securing Manual.
Hover over a part for a moment, or tap it.
Securing containers on a ship
This cross-section shows how containers are held in the hold and on deck. Hover over a part, or tap it, to see what it does.
Securing cargo inside a container
The container protects the cargo from weather but not from movement. Cargo must be packed and secured by the shipper so it survives braking trucks, rail shunting and a rolling ship.
Hover over a part for a moment, or tap it.
Securing cargo inside a container
A side view of a container with the usual securing methods. The international guide is the IMO/ILO/UNECE CTU Code (2014). Hover over a part, or tap it.
Dangerous goods and the IMDG Code
Dangerous goods are substances and articles that can harm people, the ship, other cargo or the environment: fuels, gases, paints, acids, chemicals, lithium batteries, fireworks and many more. Every one has a four-digit UN number and a class from the UN Recommendations on the Transport of Dangerous Goods (the “Orange Book”), which all transport rules share.
The 9 classes
The IMDG Code at sea
The International Maritime Dangerous Goods (IMDG) Code of the International Maritime Organization (IMO) sets the rules for dangerous goods on ships: classification, packaging, marks and labels, placards, documents, stowage and segregation. It is mandatory under SOLAS chapter VII, and its marine pollutant rules apply under MARPOL Annex III. The Code is updated every two years; Amendment 42-24 is mandatory from 1 January 2026.
Other modes have their own rules built on the same UN system: ADR for road, RID for rail in Europe, SMGS Annex 2 for rail in the 1,520 mm countries of Central Asia and Russia, and the IATA DGR for air. A transit shipment through Iran must meet the rules of every leg.
What the shipper must do
- Classify the goods and find the UN number, proper shipping name and packing group (from the safety data sheet).
- Use UN-approved packaging, and mark and label each package.
- Send the line a dangerous goods declaration and get the booking accepted before delivering the box; many lines and terminals refuse some classes.
- Have the person who packed the container sign a container packing certificate.
- Keep incompatible classes apart (segregation), secure the packages, and fix placards and marks on all four sides.
Placards and marks on the container
Hover over a part for a moment, or tap it.
Where the dangerous goods marks go
A container with dangerous goods carries marks on all four sides. Hover over a mark, or tap it.
- Acceptance is decided by the shipping line, the terminal and the port authority. Get the booking approved for the exact UN number before the container is packed.
- Send the dangerous goods declaration and the safety data sheet (SDS) with the booking. Ports usually ask for them before the ship arrives.
- Dangerous goods containers are kept in a separate area of the terminal, with limits by class. Some classes, especially explosives (class 1) and radioactive material (class 7), are normally not stored in the port and must be collected straight from the ship, with special permits.
- For transit through Iran, some dangerous goods need permits from the authorities responsible for that product before customs accepts the transit declaration. Explosives, weapons-related goods, radioactive material and some chemicals are strictly controlled.
- The road leg needs a truck and driver suitable for dangerous goods, orange plates and the right documents for every country on the route.
We check the acceptance and permits for each UN number before you book.
How strong must the securing be?
Securing is designed for the highest acceleration the cargo will meet on its route. Typical design values:
| Mode | Forward | Backward | Sideways |
|---|---|---|---|
| Road (EN 12195-1) | 0.8 g | 0.5 g | 0.5 g |
| Rail (CTU Code) | 0.5 g, 1.0 g in combined transport | 0.5 g, 1.0 g in combined transport | 0.5 g |
| Sea, rough areas (CTU Code, area C) | 0.4 g | 0.4 g | 0.8 g |
“g” is the weight of the cargo itself. A 0.8 g forward force on a 10 t machine means the securing must hold about 8 t when the truck brakes hard.
Before loading: inspect the empty container (holes, floor, door gaskets, locking bars), check the CSC plate is valid, remove old labels, and check for smells or wet spots. Take photos.
While loading: heavy items at the bottom and in the middle, no empty spaces, a barrier at the door end, and photos of each stage. Write the position of each item on the packing list.
After loading: weigh the container, check the axle loads for the road leg (road limits in Iran and the transit countries are often lower than the container's maximum gross weight), fix the seal and write its number on every document.
Problems we see at the borders: seal numbers that do not match the papers, overweight axles at weigh stations, cargo that shifted and pushes on the doors, missing dangerous goods placards, and container numbers that are hard to read. Each of these stops the truck.
General guidance, last reviewed November 2026. Rules change often; ask us to confirm the requirements for your shipment.