A chain is a series of connected links. This article is about the literal, physical chain. A chain may consist of two or more links.

A chain is usually made of metal.

Chains are usually made in one of two styles, according to their intended 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 makes the chain flexible in two dimensions.

• 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.

Chains can also be decorative as jewellery.

Uses for chain

Specific uses for chain include:

• Bicycle chain, chain that transfers power from the pedals to the drive-wheel of a bicycle thus propelling it
• Chain drive, the main feature that differentiated the safety bicycle
• Chain gun, type of machine gun that utilizes a chain, driven by an external power source, to actuate the mechanism rather than using recoil
• Chain pumps, type of water pump where an endless chain has positioned on it circular discs
• Chain-linked Lewis, lifting device made from two curved steel legs
• Chainsaw, portable mechanical, motorized saw using a cutting chain to saw wood.
• Curb chain, used on curb bits when riding a horse
• Door chain, a type of security chain on a door that makes it possible to open a door from the inside while still making it difficult for someone outside to force his or her way inside
• Keychain, a small chain that connects a small item to a keyring
• Lead shank (or "Stud chain"), used on difficult horses that are misbehaving
• O-ring chain, a specialized type of roller chain
• Roller chain, the type of chain most commonly used for transmission of mechanical power on bicycles, motorcycles, and in industrial and agricultural machinery
• Snow chains, used to improve traction in snow
• Timing chain, used to transfer rotational position from the crankshaft to the valve and ignition system on an internal combustion engine, typically with a 2:1 speed reduction.
• Ball and chain, phrase that can refer to either the actual restraint device that was used to slow down prisoners, or a derogatory description of a person's significant other
• Bicycle lock (or "Bicycle Chain"), lockable chain
• Security chain, specifically designed chain with square edges to prevent cutting with bolt-cutters.
• High-tensile chain (or "Transport chain"), chain with a high tensile strength used for towing or securing loads.
• Leg iron chains (Fetters), an alternative to handcuffs
• Chain link fencing, type of fencing that utilizes vertical wires that are bent in a zig zag fashion and linked to each other
• Chain of office, collar or heavy gold chain worn as insignia of office or a mark of fealty in medieval Europe and the United Kingdom
• Chain weapon, a medieval weapon made of one or more weights attached to a handle with a chain
• Nunchaku, karate sticks linked by a chain
• Omega chain, a pseudo-chain where the 'links' are mounted on a backing rather than being interlinked
• Pull switch, an electrical switch operated by a chain
• Flat chain, form of chain used chiefly in agricultural machinery