Padlocks are portable locks used to protect against theft, vandalism, sabotage, espionage, unauthorized use, and harm. They are designed to protect against some degree of forced and surreptitious entry.
A padlock is composed of a body, shackle, and a locking mechanism. The typical shackle is a U shaped loop of metal (round or square in cross-section) that encompasses what is being secured by the padlock (i.e., chain link or hasp). Generally, most padlock shackles either swing away (typical of older padlocks) or slide out of the padlock body when in the unlocked position. Unusually designed padlocks may include a straight, circular, or flexible (cable) shackles. Some shackles split apart and come together to lock and unlock.