A chain is a series of generally made of metal, typically of similar character, assembling links, called links, with the rope being flexible and inclined in compression but linearly rigid and load-bearing tension. A chain can consist of two or more links. Chains can be classified according to their design, which can be determined by their use:

Designed for lifting, for example when used with a crane; to draw; or for fastening, for example with a bicycle lock, it has torus-shaped links that make the chain flexible in two dimensions (the fixed third dimension is the length of a chain). Small chains that serve as jewelry are a mostly decorative analogue of these types.
Those designed for power transmission in machines have links designed to engage with the teeth of the machine's gears and are flexible in only one dimension. They are known as roller chains, but there are also non-roller chains such as blockchain.
Two different chains can be connected using one quick link , carabiner , shackle or fork . Load can be transferred from one chain to another with a chain stopper

 

Some of the most useless random disconnected footage I've ever seen on Youtube! Waste of ten minutes.