Handcuffs restrain an individual with handcuffs when the open bracelet is placed upon a body part, usually the wrist, and the ratchet is locked in place. When open, the ratchet pivots freely on a pivot. When closed, the teeth of the ratchet engage the teeth of the spring-loaded pawl located inside the bracelet. The pawl is forced against the ratchet, which locks the two sets of teeth together. To open the handcuff, the pawl must be disengaged from the ratchet teeth. This is accomplished by the handcuff key that unlocks the primary lock.

History
Handcuffs have been used as a means of restraint for several centuries. However, before 1862, they were essentially a "one size fits all" device. These early cuffs, which were simply metal rings that locked in place, created discomfort for people with thick wrists and were ineffective when used on people with thin wrists. That changed in 1862, when W. V. Adams revolutionized the device with the invention of adjustable ratchets that could bind wrists tightly or loosely. An Adams cuff consisted of a square bow with notches on the outside that engaged with a lock mechanism shaped like a teardrop. Several years later, Orson C. Phelps patented a version of the ratchet handcuff that placed the ratchet notches on the inside of the square bow.

In 1865, an entrepreneur named John Tower used the Adams and Phelps patents to start his own handcuff company. The Tower Company manufactured handcuffs until World War II, and though it always employed the Adams patent, its products set the standards for precision, craftsmanship and effectiveness. The first Tower cuff was based on the Phelps design, with notches on the inside and a three-link chain connecting the two cuffs. The second cuff was more similar to the Adams handcuff. The keyhole location was moved from the side of the lock case to the bottom, and it featured a round bow. Also, it featured three round rings between the cuffs, instead of a chain. The outer two rings were perfectly round while the middle ring was bent, just like the rings on the Adams cuff. In addition, the lock case of this second cuff was smaller. Tower applied for his first handcuff patent in 1871. His design innovation was a round bow meant as an improvement to the square bow of the Phelps and Adams cuffs. The patent was finally issued in 1874.

With the adjustable-fit handcuffs, a design flaw was evident: the spring loaded mechanism that allowed the cuffs to be adjustable also allowed the cuffs to be tampered with so that the restrained person would be able to spring the lock and escape. Tower solved that problem with the introduction of the double lock handcuff, which he patented in 1879. The lock had two settings: a single-lock mode and double-lock mode. The first mode acted just like a single-lock handcuff. The user could turn the key clockwise to set the cuff into double-lock mode, which froze that catch or bolt, effectively preventing any escaping. The double lock model set the standard both for effectiveness and engineering.

Throughout the nineteenth and twentieth centuries, the handcuff industry continued to change and handcuff design innovations were implemented. One inventor (E. D. Bean in 1882) created a release button to keep the locking mechanism from engaging until the officer released a button and then the cuffs were locked. This mechanism''s purpose was to stop cuffs from closing and locking (during a struggle, for example) before the officer could get the cuffs around the offender''s wrists. This problem was more effectively solved by another inventor''s patent for a swing-through ratchet. This design ensured that the cuffs would not lock unless placed on a wrist. The resulting Peerless cuffs (patented in 1912) set a new standard for the handcuff industry, and became the model for modern cuffs.

Raw Materials
Raw materials include chrome steel, nickel plating ,cuff plating, and metal springs.

Design
Handcuffs typically do not vary much from the standard. A standard pair of modern handcuffs weighs no more than 15 oz (425 g). The minimum opening of the bracelet is 2 in (5 cm). The minimum inside perimeter of the bracelet is 7.9 in (20 cm) when the ratchet is engaged at the first notch. The maximum perimeter is 6.5 in (16 cm) when the ratchet is engaged at the last notch. The maximum overall length of the handcuffs is 9.4 in (24 cm).

The Manufacturing
Process
Handcuff manufacturing starts with the construction of each shackle bracelet. The bracelet consists of three separate parts: the cheek plates, the ratchet (a cheek bar with inclined teeth designed to engage the pawl), and the pawl. The bracelet is made from molten chrome steel poured into a mold and cooled. Once the steel has cooled, it is taken out of the mold.
A spring-loaded pivot bar is then constructed inside each bracelet, also made out of steel.
The ratchets are constructed in the same format as the cheek plate. The rotatable shackle bracelet, including ratchet teeth, is attached to the shackle base at a protruding end of a shackle base. The ratchet is designed to advance in only one direction.
The shackle base is also molded from molten steel and includes a flat keyhole.
The shackle bracelet is jointed to the protruding shackle end at a pivot. This permits the shackle bracelet to rotate about the pivot relative to the shackle base.
Next, the shackle bracelet end is shaped and dimensioned.
The two ring-shaped shackle bracelets are then connected to a short chain. The chain is welded at either end to the shackle base of each handcuff.
At the conclusion of the manufacturing process, the handcuffs are marked with the manufacturer''s name or trademark, model number, and serial number.