A chain is a serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear, rigid, and load-bearing in tension. A chain may consist of two or more links. Chains can be classified by their design, which can be dictated by their use:
Those designed for lifting, such as when used with a hoist; for pulling; or for securing, such as with a bicycle lock, have links that are torus shaped, which make the chain flexible in two dimensions (the fixed third dimension being a chain's length). Small chains serving as jewellery are a mostly decorative analogue of such types.
Those designed for transferring power in machines have links designed to mesh with the teeth of the sprockets of the machine, and are flexible in only one dimension. They are known as roller chains, though there are also non-roller chains such as block chain.
A common metal short-link chain
Two distinct chains can be connected using a quick link, carabiner, shackle, or clevis.
Load can be transferred from a chain to another object by a chain stopper.
Lead shank (or, stud chain), used on horses that are misbehaving
Pull switch, an electrical switch operated by a ball chain
Lavatory chain, the chain attached to the cistern of an old-fashioned W.C. in which the flushing power is obtained by a gravity feed from above-head height. Although most cisterns no longer work like that, the phrase "pull the chain" is still encountered to mean "flush the toilet".
Rigid chain actuator, a type of chain that only bends in one direction, allowing it to operate under compression
Roller chain, the type of chain most commonly used for transmission of mechanical power on bicycles, motorcycles, and in industrial and agricultural machinery
Silent chain, a type of chain in which the links engage the sprockets similarly to gear teeth
Stud link chain is chain with metal between the sides of each link keeping the attached links in place. This helps prevent bunching when the chain is run out from a storage bin, as for use in anchoring ships.
Short link chain is chain where the gap between attached links is small relative to thickness.
Long link chain
Calibrated chain is chain where the link lengths are within a given tolerance, so that it reliably engages with a windlass.
Several methods are available to connect chain ends to each other or to other objects, and to apply a load to a chain away from the ends. These methods are usually specific to the type of chain, and must be of the correct size.
The metal link chain has been in use since at least 225 BC.
The prevalent modern symbolism is oppression, due to the use for a mechanical restriction of the liberty of a human or animal.
^As early as 225 BC, chain was used to draw a bucket of water up from a well. This very early bucket chain was composed of connected metal rings.Tsubakimoto Chain Co., ed. (1997). The Complete Guide to Chain. Kogyo Chosaki Publishing Co., Ltd. p. 240. ISBN 0-9658932-0-0. p. 211. Retrieved 17 May 2006.
National Association of Chain Manufacturers, NACM WELDED STEEL CHAIN SPECIFICATIONS