Since the invention of the highly-effective ratcheted handcuff model, patented by W.V. Adams in 1862, nearly every style of handcuffs sold has used some version of the ratchet design. The primary differences among modern handcuffs, aside from brand variances in lock design, lie in the way the two separate cuffs are connected. The three main styles of ratchet handcuffs in use today are chain cuffs, hinge cuffs, and cuffs connected with a rigid bar.
Chain cuffs are by far the most popular cuffs for everyday use in law-enforcement due to their ease of application (even on a struggling subject) and the fact that they can be folded in half for better portability. The two cuffs are attached by a short chain, typically just two links long, and the ratchet arms are usually swing-through for even greater ease and speed of application: they can be applied to the subject’s wrist with just one hand.
Hinged cuffs are very similar to chain cuffs in every capacity save the connection point: they are attached by a hinge rather than a chain. Hinge cuffs are shorter than chain cuffs when extended, thus allowing for less movement on the part of the subject. This makes them potentially more secure, but more also potentially more difficult to apply if the subject is in motion. Many law enforcement officers find that the solution to this problem, if one wrist has been cuffed but the subject is non-compliant, is the ability to apply uncomfortable torque on the cuffed wrist as a method of persuasion. This method of eliciting compliance would be difficult or impossible with the more flexible chain cuffs.
The third most common type of cuff is connected by a rigid solid bar. When actively used on a subject, they function more like hinged cuffs, holding the hands closer together than chain cuffs and providing the least mobility for the subject. This makes them more secure than chain cuffs, but the downside is that they are also more difficult to carry even than hinged cuffs because they cannot be folded in half. Rigid bar cuffs, like hinged cuffs, allow the law enforcement officer to apply pain-compliance techniques that aren’t possible with chain cuffs. Where chain cuffs are more likely to be used during an initial arrest, rigid bar cuffs may be used when transporting a subject from one place to another, particularly if the subject is known to be non-compliant.
What all of these cuffs have in common is the potential to be opened with a universal handcuff key such as TIHK. Regardless of the type of connection between the two cuffs, most modern handcuffs have a very simple lock design for practical reasons. As a result, a universal cuff key may very well be able to open chain cuffs, rigid bar cuffs, and hinged cuffs, though ease of use may vary according to the varied mobility provided by the different styles. Variations in manufacturing and lock styles notwithstanding, TIHK can open every one of these types of handcuffs.