Dimple Locks: Pin Tumblers Read from the Face of the Key

How a Dimple Lock Works

Inside, a basic dimple lock works like any pin tumbler. Lockwiki explains that the plug "may rotate when dimples in the key properly position a number of pin-tumbler stacks at the shear line." The difference is "the orientation of the keyway and the location and style of the bitting cuts on the key blade." Each dimple's depth sets one pin stack, just as each notch on an edge-cut key does.

Depths, Positions and Key Length

Moving the cuts to the key's face changes what designers can do with it. Lockwiki describes the tradeoff:

• Fewer depths per pin. Because the key is thin, dimple locks "generally allow two to six depths per pin." Traditional pin tumblers allow "anywhere from six to twelve positions per pin."
• More pin positions. Modern dimple locks can place pins "on all sides of the key." That greatly increases the number of positions available, which Lockwiki ties to greater key control and master keying capability.
• Shorter keys. Edge-cut keys "have problems with increasing the number of pins because the key must be extended." Past about seven or eight pins, Lockwiki says, they "become too long and have problems with bending and breaking."

Added Security Features

The basic dimple layout is often combined with other features. Lockwiki lists key profiling, side pins, telescoping pins and axial rotation, plus "additional passive and active locking mechanisms" such as sidebars and moving elements inside the key. Profiles and keyways are covered under restricted keyways and key blanks and keyways.

Lockwiki also cautions that "a dimple lock is not more secure when compared to traditional pin tumbler locks, but the untraditional nature of the key makes many dimple locks appear sophisticated". Security depends on the specific product and its testing; see EN 1303, UL 437 and high-security locks.

Kaba and the Reversible Key

Kaba, now part of dormakaba, gives one of the best-documented histories for this design. dormakaba traces its Kaba side to an 1862 "locksmith shop and cash register factory set up by Franz Bauer near Zurich." Its timeline lists "1934: Patenting of reversible key."

The Swiss newspaper Neue Zürcher Zeitung gives more detail in a 2005 article. The original system, the Kaba 8, was invented in 1934 by Fritz Schori, a tinkerer and works manager at the safe maker Bauer in Wetzikon. NZZ describes the key as having no teeth and no top or bottom. Instead it had hole-like recesses on both broad sides of the shaft. Schori knew the Yale lock. In his patent he criticized the fact that the Yale key cannot be inserted upside down. His answer was the reversible-key principle. See Linus Yale.

NZZ adds that sales were slow at first, partly because carpenters had drills and templates for the slimmer Yale cylinders. The Second World War changed that. Switzerland could no longer import Yale locks, and carpenters switched to the wider domestic Kaba cylinders and stayed with them after the war.

This article does not claim Kaba invented the dimple lock. The sources found here describe Kaba's reversible key, not a first dimple lock.

A current Kaba design shows how far the layout can go. dormakaba's quattro factsheet (technical version K94) describes a reversible key with "4 radially arranged tumbler pin rows with up to 22 pairs of pins." It also lists patent protection and a "coded drilling pattern" in which certain tumbler pin positions "are not visible on the key."

Mul-T-Lock and Telescoping Pins

A second lineage comes from Israel. According to a technical history on LockpickingForensics.com, Mul-T-Lock was founded in 1973 by Avraham Bachri and Moshe Dolev. It began with a 1972 request to install "four extra locks for her front door," which led the two to design a multi-point locking system. ASSA ABLOY bought Mul-T-Lock in 2000. ASSA ABLOY says Mul-T-Lock products are sold through distribution in 80 countries.

The same source says Mul-T-Lock is best known for dimple locks with telescoping pin pairs, or "pin-in-pin." In these locks an outer pin pair surrounds an inner pair, and "both inner and outer tumblers must be properly aligned at the shear line." The idea is older than the company:

• Thorsten Rydberg's 1897 patent describes tumblers made of a pin "surrounded by one, two, or more concentric tubes."
• A 1914 patent to Christian Hansen of Davenport, Iowa, used telescoping pin pairs.

Lockwiki states that Mul-T-Lock began using telescopic pins in 1977 and credits Mul-T-Lock and KESO with popularizing the design.

Other Makers

Lockwiki names KABA, Mul-T-Lock, DOM, LIPS, GOAL and KESO among the best-known dimple lock makers. For the cylinder housing common in Europe, see euro cylinders. This article does not describe ways of opening dimple locks without a key.

Related Topics

• Pin tumbler locks
• Restricted keyways
• Key blanks and keyways
• Key control
• Master keying
• Sidebar locks
• Euro cylinders
• EN 1303
• UL 437
• High-security locks
• Linus Yale
• Magnetic keyed locks

Sources