The female part of the connector is the 7″×7″×4⅔″ corner casting fitted to the container itself, and which has no moving parts, only an oval hole in the bottom. The hole is a 4.9″ diameter circle with two flat sides 2.5″ apart.
The male component is the twistlock, which is fitted to cranes and transport bases. This can be inserted through the hole it is roughly 4.1″ long and 2.2″ wide, and then the top portion normally pointed to make insertion easier is rotated 90° so that it cannot be withdrawn. The mechanism is the same as that of a Kensington lock, on a much larger scale.
