Padlocks are used throughout the world to safeguard possessions are prevent unwanted entry. While no-one knows exactly where padlocks were invented, evidence of their use stretches back to ancient Roman times. However, padlocks were also used in China and throughout Asia, where ancestors to the modern padlock form are likely to have existed in even earlier times.
While the design of padlocks has changed a lot throughout history, the basic components have remained much the same. Modern padlocks are composed of a body made from metal, a shackle, and a locking mechanism.

Shackle and Lock

The normal shackle that is used in pad locks (Vorhangschlösser) is a U shaped metal loop, which can come in both round and square shapes. The shackle encompasses what ever is being secured by the padlock, with chain links being one of many possibilities. Most padlock shackles either swing away or slide away from the main padlock body, but can only do so while the padlock is in an open and unlocked position. While most padlocks on the market feature a similar form and are made from the same basic shackle cross-section, there are some more unique locks out there that feature circular or flexible cable shackles. In terms of the locking mechanism itself, there are two basic types that are used, integrated and modular. While integrated locking mechanisms engage the shackle directly with locking tumblers, the more modern modular designs have a cylinder mechanism instead.

In contrast to the integrated or ‘Scandinavian’ mechanisms that have been used four hundreds of years, modern modular components do not directly employ the lock tumblers to lock the shackle. Instead, a mechanism known as the ‘locking dog’ is turned by the key in order to retract notches that are cut into the shackle. While many padlocks today are inexpensive and not designed to be worked on, some larger and more complex locks can be serviced through changing the tumblers and adjusting the other components. Modern modular padlock mechanisms often use cylinders with pin, wafer, and disk tumblers, and are mostly designed to function in an automatic, self-locking fashion.