Twistlock

A twistlock and corner casting together form a standardized rotating connector for securing shipping containers. The primary uses are for locking a container into place on a container ship, semi-trailer or railway container train, and for lifting of the containers by container cranes and sidelifters.
Description.
The twistlock was developed in Spokane, Washington in the 1950s by transport engineer Keith Tantlinger. The relative obscurity of this invention belies its importance to a more efficient world trade and transport, as the Tantlinger lock made handling and stacking standard containers much easier.
A major advantage of this approach to attachment is that containers, which may be stored or transported without being inspected for months at a time, do not require any maintenance in order to function effectively. Even with long term exposure to the weather the container remains as simple to move as ever. Only when corrosion is very extensive (to the extent of being easily visible) does the twistlock become dangerous to move the crate. The male part (which is more exposed and susceptible to damage) is placed on vehicles and equipment that are inspected very frequently, and will work with all standard containers.
Mechanism.
The female part of the connector is the corner casting, which is fitted to the container itself, and has no moving parts, only an oval hole in the bottom. The hole is an oval on the long axis with two flat sides 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 long and wide), and then the top portion (normally pointed to make insertion easier) is rotated 90° so that it cannot be withdrawn. The mechanism is similar to 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 ISO 1161:1984. The tensile strength of a twistlock is rated at either 20 or 25 tonnes.
Some twistlocks have built-in levers or mechanisms, while simpler versions require tools for installation or removal. Some twistlocks are permanently installed (e.g. on the decks of container ships or on the beds of semi-trailers), while others are temporarily installed and removed as needed (e.g. to stack containers in storage yards). 
Applications.
Special types of twistlocks are also used in double-stack rail transport to secure the lower stack container with the upper one.