Padlocks: Portable Locks from Barb-Springs to Laminated Steel

Parts and Terms

LIST defines the hardware a padlock works with:

• Shackle. The movable loop that passes through the item being secured and locks into the case.
• Hasp. "A hinged metal strap designed to be passed over a staple and secured in place."
• Staple. "The portion of a hasp assembly with the hole or opening to receive a padlock."
• Padlock eyes. Fixtures "with a hole to receive the shackle of a padlock. Usually used in pairs."
• Heel and toe locking. A padlock "which has locking dogs at both the heel and toe of the shackle." Both legs of the shackle are held, not just one.
• Shrouded shackle. "A shackle which is protected from cutting or tampering by design or by the use of secondary shields."
• Key retaining. A lock "which must be locked before its key can be removed." Some padlocks are made this way so the key cannot be removed while the shackle is open.

The locking mechanism inside the case can be almost anything: warded, lever tumbler, pin tumbler, disc detainer, or combination. The padlock is a form, not a mechanism.

Early Padlocks: The Barb-Spring Design

The Portable Antiquities Scheme (PAS), which records archaeological finds in England and Wales, says "padlocks seem to have been first used in Britain in the very late Iron Age or early Roman period."

PAS explains that "most padlocks in the past were held together with barb-springs (also called leaf-springs)." The design has two halves:

• The case. This is hollow, open at one end, and has a keyhole at the other.
• The bolt. This is a spine carrying two strips of springy metal fixed at one end "to form a barbed arrowhead shape."

When the bolt is pushed into the case, the springs squeeze together. Once they clear the end of the case, they spring apart and lock the bolt in place. To open it, a key shaped to fit the keyhole slides along the springs and squeezes them together so the bolt can be withdrawn.

PAS also describes medieval iron padlocks, usually "a cylindrical iron case covered in a thin plating of copper alloy." It classifies medieval finds by case shape, and notes that "the tubular case is the commonest shape for medieval padlocks."

Harry Soref and the Laminated Padlock

LIST defines a laminated padlock as "a padlock whose case is constructed of separate plates usually riveted together." The best-known example in the United States is the Master Lock padlock.

• The company. Harry Soref founded the Master Lock Company in Milwaukee in 1921, "with investments from two friends," according to the Encyclopedia of Milwaukee. Smithsonian Magazine gives the same founding year.
• The patent. Soref's U.S. Patent 1,490,987, "Lock Casing," was filed October 3, 1921 and granted April 22, 1924.
• How the case is built. The patent describes a casing "constituted as a laminated structure," made by punching the sections in a press so that no milling or machining is needed after assembly. The laminations "are secured together by means of rivets." Some laminations "act as wards," so that only the matching key can operate the lock. The patent also notes the laminations can be "punched from the small scrap" that factories with punching presses produce in large quantities.
• Why it mattered. Smithsonian Magazine says that before 1921 locks came in two styles: "expensive but nearly impossible to break and cheap but easy to smash open." The laminated case aimed at both strength and low cost.

Master Lock's own timeline lists its first combination lock in 1935 and its first resettable combination lock in 1982. Per the Encyclopedia of Milwaukee, Soref died in 1957. The company was sold to American Brands (later renamed Fortune Brands) in 1970 and spun off with Fortune Brands Home & Security in 2011, and its Milwaukee plant closed in 2024. See Harry Soref.

Standards and Grades

Padlocks are graded under their own standards, separate from door-lock grades.

ASTM F883 (United States). ASTM's scope for F883, Standard Performance Specification for Padlocks, includes "function descriptions, cycle tests, operational tests, environmental tests, forcing tests, and surreptitious entry tests." It "describes and grades various levels of performance" so users can select suitable padlocks. ASTM notes the tests "simulate field conditions… they do not duplicate these conditions." Manufacturers cite F883 grades in catalogs. American Lock, for example, calls Grade 6 "the highest performing grade level" for a padlock product. The full grade tables are in the paid standard.

BS EN 12320 (Europe/UK). BSI's summary of the 2021 edition says it "establishes one category of use, two categories of durability, six categories for corrosion resistance and six grades for security based on performance tests that simulate an attack."

Sold Secure SS 303 (UK). Sold Secure was set up in 1992 by Northumbria and Essex Police and is now administered by the Master Locksmiths Association. Its 2024 catalogue lists the SS 303 padlock specification as "harmonised with BS EN 12320," mapping Bronze to CEN 3, Silver to CEN 4, Gold to CEN 5, and Diamond to CEN 6. Sold Secure adds that approval "is only valid when a product is fitted correctly."

See also high-security locks.

Combination and Disc-Type Padlocks

• Combination padlocks open without a key. Master Lock dates its first combination lock to 1935 and its first resettable one to 1982. See combination locks.
• Disc detainer padlocks. See disc detainer locks and Abloy.
• Keyed padlocks in systems. American Lock's catalog, for example, says its rekeyable cylinders "can be keyed differently, alike, master keyed or grand master keyed." See master keying and key control.

Related Topics

• Harry Soref
• Warded locks
• Lever tumbler locks
• Pin tumbler locks
• Disc detainer locks
• Combination locks
• Abloy
• UL 437
• High-security locks
• Key control

Sources