Padlock

Padlocks are portable locks with a shackle that may be passed through an opening (such as a chain link, or hasp staple) to prevent use, theft, vandalism or harm.

[3] They were known in early times by merchants traveling the ancient trade routes to Asia, including China.

[4] Padlocks have been used in Europe since the middle La Tène period, subsequently spreading to the Roman world and the Przeworsk and Chernyakhov cultures.

[6] Padlocks with spring tine mechanisms have been found in York, England, at the Jorvik Viking settlement, dated 850 AD.

[7] Smokehouse locks, designed in England, were formed from wrought iron sheet and employed simple lever and ward mechanisms.

These lock shells were stamped out of flat metal stock, filled with lever tumblers, and then riveted together.

In 1877 Yale & Towne was granted a patent for a padlock that housed a stack of levers and had a shackle that swung away when unlocked.

It was a notable design because the levers were sub-assembled into a "cartridge" that could be slid into a cast brass body shell.

About twenty years later Yale made another "cartridge" style padlock that employed their famous pin tumbler mechanism and a shackle that slid out of the body instead of swinging away.

Many machined body padlocks were designed to be disassembled so that locksmiths could easily fit the locks to a certain key.

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 (e.g., chain link or hasp).

Examples of integrated locking mechanisms are rotating disks (found in "Scandinavian" style padlocks where a disk rotated by the key enters a notch cut into the shackle to block it from moving) or lever tumblers (where a portion of the bolt that secures the shackle enters the tumblers when the correct key is turned in the lock).

A padlock was invented by John I. W. Carlson in 1931 (a patent was granted in November 1934) that has both a combination on one side and a key on the other.

Padlocks with a flexible cable shackle have been made to encompass larger or irregular things such as a bicycle, gate, or even the zippers on backpacks and luggage.

Typically used by vending companies, such cable shackle padlocks prevent the surreptitious removal of a key for duplication or unauthorized use outside of working hours.

A quantitative measure of a padlock's tensile strength and resistance to forced and surreptitious entry can be determined with tests developed by organizations such as ASTM, Sold Secure (United Kingdom), CEN (Europe), and TNO (The Netherlands).

In some popular tourist locations, huge numbers of such padlocks are treated as a nuisance by local authorities.