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Electrical Safety·July 1, 2023

The History of Padlocks: Who Invented Them and When

Who invented the padlock, when, and why is it called that? A short history of padlocks, from barbed springs to the personal lockout padlock used in maintenance.

The History of Padlocks: Who Invented Them and When

The history of padlocks goes back at least 2,200 years: the oldest complete barbed-spring lock found so far comes from the mausoleum of China's First Emperor and dates from the 3rd century BC.[1] At work today, its most important job is lockout: a personal lock on each isolation point, so nobody can restart a machine while someone works on it.

Table of Contents
  1. When Were Padlocks Invented, and by Whom?
  2. The History of Padlocks at a Glance
  3. Why Is It Called a Padlock?
  4. Padlocks in the Middle Ages and After
  5. Linus Yale and the Pin-Tumbler Cylinder
  6. From Padlock to Lockout Padlock
  7. Where The Lock Box Fits

This post answers four questions:

  1. When were padlocks invented, and who invented them?
  2. Where does the word "padlock" come from?
  3. How did the mechanism change, from springs to pin tumblers?
  4. What makes a lockout padlock different from the padlock on a locker?

Part 1: When Were Padlocks Invented, and by Whom?

Padlocks were in use in China by the 3rd century BC, and in Britain before the Roman conquest. No inventor is known: the earliest padlocks are archaeological finds, not patents.

The oldest complete Chinese example comes from the mausoleum of the First Qin Emperor.[1] In Britain, iron barb-spring padlocks were in use from the Late Iron Age and have been found at several Roman sites.[2]

The idea is simple. The bolt, or shackle, carries flat springs that work like fish hooks: they slide into the case, spread out and catch. The bolt cannot come out until the key squeezes the springs flat again.[3] By around 200 AD, this flat-spring padlock was a familiar design in China.[3]

Padlocks became the most common lock in ancient China because they were easy to carry. A long, straight shackle passed through two rings on a door or a box. Chinese locksmiths also made puzzle padlocks that opened only in a set sequence of steps, even with the right key.[1]

Part 2: The History of Padlocks at a Glance

When Where What changed
3rd century BC China Oldest complete barbed-spring lock found so far
Late Iron Age to Roman period Britain Iron barb-spring padlocks in use
Around 200 AD China Flat-spring padlock a familiar design
1100 to 1400 England Barb-spring padlocks still in use
17th century Europe Large iron padlocks, such as one of 21 cm in the Met
1865 United States Linus Yale Jr. patents improvements to pin-tumbler locks
Today Workplaces Lockout padlocks: one personal lock per worker

The last row is a different tool: our lockout padlocks protect the person working on a machine (Part 6).

Part 3: Why Is It Called a Padlock?

A padlock is a portable lock with a pivoting or sliding shackle that passes through a link, ring or staple.[4] The word is late Middle English, "padlok", first recorded between 1425 and 1475.[4]

So why is it called a padlock? Nobody knows for certain. The "lock" is plain; the origin of "pad" is uncertain.[4] Unlike a door lock, a padlock is not built into what it secures, so it can be carried to a chest, a gate or an isolation point.

Part 4: Padlocks in the Middle Ages and After

The barb-spring padlock outlived Rome by a long way. A barb-spring padlock found in Norfolk, England, is dated 1100 to 1400.[5]

Surviving European padlocks from the 16th to the 18th century are often iron or steel. A 17th-century iron padlock in the Metropolitan Museum of Art measures 21 by 7 cm.[6] For comparison, the body of our 38 mm lockout padlocks measures 45 by 37 mm.

These padlocks guarded chests, gates and stores against theft. A lockout padlock has a different brief: it must identify its owner and open only with its own key.

Part 5: Linus Yale and the Pin-Tumbler Cylinder

Linus Yale Jr. (1821-1868) made innovations in lock making that became the basis for the modern key and tumbler lock.[7] He invented the first modern cylinder lock: a pin-tumbler mechanism, a principle already known in ancient Egypt, turned by a small flat key with serrated edges.[7]

His patent of 27 June 1865 covers improvements to pin locks, including the cylinder and the tumbler case.[8]

In a pin-tumbler cylinder, spring-loaded pins of different lengths block the plug. Only the right key lifts every pin to the line where the plug can turn. Cut each key differently and each lock has its own key. On a lockout padlock, that is what "keyed different" means.

Part 6: From Padlock to Lockout Padlock

In maintenance, the padlock protects the person, not the property: it holds an isolation device in the off position. That job comes with rules:

  • EU: the Machinery Directive 2006/42/EC, Annex I, section 1.6.3, requires isolators that can be locked if reconnection could endanger persons.[9] Regulation (EU) 2023/1230 replaces the Directive from 20 January 2027.[10]
  • Switzerland: Suva's eight vital rules for maintenance, rule 3: before work, the worker switches off all energy sources and secures the installation with their personal padlock.[11]
  • France: INRS guide ED 6109 asks for a dedicated locking device that is hard to defeat and easy to identify; with a multi-lock device, it is one worker, one key.[12]
  • US, for comparison: OSHA 29 CFR 1910.147, in force since 1989, requires lockout devices that are durable, standardised by colour, shape or size, substantial, and that identify the person who fitted them.[13]

In practice, a lockout padlock is keyed different, issued to one person, marked with a colour and a name, and used for nothing else. Some models also keep the key captive while the shackle is open, so a lock cannot be left open with the key gone. Our guide to LOTO padlocks versus normal padlocks covers the differences, and the steps of lockout tagout show where the lock goes in the sequence.

Best Practice: Give each worker their own lockout padlocks, marked with their name, and keep them for lockout only. INRS advises against using standard toolbox or locker padlocks for lockout.[12]

Part 7: Where The Lock Box Fits

Our safety padlocks for lockout tagout come with nylon, steel, aluminium or brass bodies. Three of them:

For choosing between them, see our guide to personal lockout tagout padlocks. A padlock protects only the points a procedure names, so write those points down for each machine with our free lockout/tagout procedure template (PDF, Word or Excel).

Need Padlocks for Your Team?

Contact The Lock Box with the number of workers and isolation points on your site, and we will suggest padlocks and a colour scheme for your lockout procedure.

References

  1. Zhang, Y., Wang, H.-T., Lin, J.-L., Huang, C.-F. and Hsiao, K.-H. Structural analysis of traditional Chinese blocked-keyhole padlocks. Mechanical Sciences 13, 791-802 (2022). https://ms.copernicus.org/articles/13/791/2022/
  2. Amgueddfa Cymru, Museum Wales. Iron Age / Roman iron barb sprung lock, item 2000.45H/1.117, Castell Henllys. https://museum.wales/collections/online/object/21059e8e-f0e7-3382-aa99-293507d95461/
  3. Hsiao, K.-H. Structural analysis of traditional Chinese hidden-keyhole padlocks. Mechanical Sciences 9, 189-199 (2018). https://ms.copernicus.org/articles/9/189/2018/
  4. Dictionary.com. Padlock: definition and origin. https://www.dictionary.com/browse/padlock
  5. Norfolk Heritage Explorer. NHER 66577: Medieval barb-spring padlock, 1100 to 1400 AD. https://nhe.esdm.co.uk/Monument/MNF75424
  6. The Metropolitan Museum of Art. Padlock, 17th century, iron, 21 x 7 cm, accession 87.11.47. https://www.metmuseum.org/art/collection/search/186848
  7. National Inventors Hall of Fame. Linus Yale Jr. https://www.invent.org/inductees/linus-yale-jr
  8. Yale, L. Jr. Improvement in locks. US Patent 48,475, 27 June 1865. https://patents.google.com/patent/US48475A/en
  9. EUR-Lex. Directive 2006/42/EC on machinery, Annex I, section 1.6.3 (Isolation of energy sources). https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32006L0042
  10. European Commission. Machinery: Regulation (EU) 2023/1230 applies from 20 January 2027. https://single-market-economy.ec.europa.eu/sectors/mechanical-engineering/machinery_en
  11. Suva. Acht lebenswichtige Regeln für die Instandhaltung (84040.D, in German, also in French and Italian), rule 3, revised March 2022. https://www.suva.ch/84040.d
  12. INRS. ED 6109: Consignations et déconsignations, 3rd edition, October 2020, pp. 11 and 17. https://www.inrs.fr/dam/inrs/CataloguePapier/ED/TI-ED-6109.pdf
  13. OSHA. 29 CFR 1910.147: The control of hazardous energy (lockout/tagout), paragraph (c)(5)(ii); first published 54 FR 36687, 1 September 1989. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.147
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