A twistlock and corner casting together form a standardised rotating connector for securing shipping container

Intermodal container

An intermodal container is a standardized reusable steel box used for the safe, efficient and secure storage and movement of materials and products within a global containerized intermodal freight transport system...

s. The primary uses are for locking a container into place on container ship

Container ship

Container ships are cargo ships that carry all of their load in truck-size intermodal containers, in a technique called containerization. They form a common means of commercial intermodal freight transport.-History:...

, semi-trailer truck

Semi-trailer truck

A semi-trailer truck, also known as a semi, tractor-trailer, or articulated truck or articulated lorry, is an articulated vehicle consisting of a towing engine , and a semi-trailer A semi-trailer truck, also known as a semi, tractor-trailer, or (in the United Kingdom and Ireland) articulated truck...

 or railway container train; and for lifting of the containers by container cranes and sidelifters.

The female part of the connector

Gender of connectors and fasteners

In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally assigned the designation male or female...

 is the 7 x 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 in (124.5 mm) diameter circle with two flat sides 2.5 in (63.5 mm) 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 in (104.1 mm) long and 2.2 in (55.9 mm) wide), and then the top portion (normally pointed to make insertion easier) is rotated 90° so that it cannot be withdrawn.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, but on a much larger scale.

The maximum size and position of the holes in the connector is defined in international standard

International standard

International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...

ISO 1161:1984.