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Handcuffs are restraint devices designed to secure an individual's wrists close together. They comprise two parts, linked together by a chain, a hinge, or rigid bar. Each half has a rotating arm which engages with a ratchet that prevents it from being opened once closed around a person's wrist. Without the key, the handcuffs cannot be removed and so the handcuffed person is unable to move his or her wrists more than a few centimetres/inches apart, making many tasks difficult or impossible. This is usually done to prevent suspected criminals from escaping police custody.

There are three main types of contemporary metal handcuffs: chain (cuffs are held together by a short chain), hinged (since hinged handcuffs permit less movement than a chain cuff, they are generally considered to be more secure), and rigid solid bar handcuffs. While bulkier to carry, rigid handcuffs permit several variations in cuffing. Hiatts Speedcuffs are rigid handcuffs used by most police forces in the United Kingdom. Both rigid and hinged cuffs can be used one-handed to apply pain-compliance/control techniques that are not workable with the chain type of cuff. Various accessories are available to improve the security or increase the rigidity of handcuffs, including boxes that fit over the chain or hinge and can themselves be locked with a padlock.

In 1933 the Royal Canadian Mounted Police used a type called "Mitten Handcuffs" to prevent criminals from being able to grab an object like the officer's gun. While used by some in law enforcement it was never popular.

Handcuffs may be manufactured from various metals, including carbon steel, stainless steel and aluminium, or from synthetic polymers.

Sometimes two pairs of handcuffs are needed to restrain a person with an exceptionally large waistline because the hands cannot be brought close enough together; in this case, one cuff on one pair of handcuffs is handcuffed to one of the cuffs on the other pair, and then the remaining open handcuff on each pair is applied to the person's wrists. Oversized handcuffs are available from a number of manufacturers.

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Wikipedia