Metal Handcuffs are restraint devices designed to secure an individual's wrists close together. They comprise two parts, linked together by achain, 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/Army custody.
There are three main types of contemporary metal handcuffs: chain (handcuffs 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.
The National Museum of Australia has a number of handcuffs in its collection dating from the late 19th and early 20th centuries. These include'T'-type 'Come Along', 'D'-type and 'Figure-8' handcuffs.
Handcuffs with double locks have a detent which when engaged stops the cuff from ratcheting tighter to prevent the wearer from tightening them. Tightening could be intentional or by struggling; if tightened, the handcuffs may cause nerve damage or loss of circulation. Also some wearers could tighten the cuffs to attempt an escape by having the officer loosen the cuffs and attempting to escape while the cuffs are loose. Double locks also make picking the locks more difficult.There exist three kinds of double locks as described in a Smith & Wesson brochure:-
Movement of a lever on the handcuff causes the detent to move into a position that locks the bolt. No tool is required to double lock this type of cuff.
A small peg on the key is inserted endwise into a hole to engage the detent.
These also are actuated with a peg, but in this case it is inserted into a slot and moved sideways to engage the detent.
Double locks are generally disengaged by inserting the key and rotating it in the opposite direction from that used to unlock the cuff.
Because a person's hands are used in breaking falls, being handcuffed introduces a significant risk of injury if the prisoner trips or stumbles, in addition to injuries sustained from overly tight handcuffs causing handcuff neuropathy. Police officers having custody of the person need to be ready to catch a stumbling prisoner.
As soon as restraints go on, the officer has full liability. The risk of the prisoner losing balance is higher if the hands are handcuffed behind the back than if they are handcuffed in front; however, the risk of using fisted hands together as a weapon increases with hands in front.
Some prisoners being transported from custody to outside locations, for appearances at court, to medical facilities, etc., will wear handcuffs augmented with a belly chain. In this type of arrangement a metal, leather, or canvas belt is attached to the waist, sometimes with a locking mechanism. The handcuffs are secured to the belly chain and the prisoner's hands are kept at waist level. This allows a relative degree of comfort for the prisoner during prolonged internment in the securing device, while providing a greater degree of restriction to movement than simply placing the handcuffs on the wrists in the front.