How Do Twist Locks Work?

The male part of a twist lock is fitted to vehicles and equipment and will normally work with any standard containers. It’s more exposed, too, making it more prone to damage. Meanwhile, the female part is called the corner casting, which has no moving parts. It has an oval hole in the bottom and is attached to the container itself.

The hole is roughly 5 inches long with two flat sides about 2 ½ inches apart. The male part of the container twist lock, which is fitted in bases and cranes, is inserted through the hole and usually has a pointed top portion to make insertion easier. It’s then rotated 90 degrees so it can’t be withdrawn. The maximum size and placements of holes in the corner castings are defined by international standards and the ultimate tensile strength of twist locks is rated at 20 or 25 tons.

Simpler versions of twist locks use tools for installing and removing them while modern versions already have built-in levers or mechanisms. Some twist locks can be installed permanently (i.e. on the beds of semi-trailers or on the deck of container ships) while some are installed temporarily so they can be easily removed when needed (i.e. to stack containers in storage yards.)