Lever

Lever

A lever (or lever tumbler) is a lock design that uses flat pieces of metal (also known as levers) and a bolt as locking components. In most designs, the position of the levers prevents the bolt from retracting. When positioned properly, a gate in the lever allows the bolt to retract. Lever locks are historically one of the most popular lock designs, but use has dwindled as less expensive pin-tumbler locks have gained popularity. Lever locks are popular in Europe (specifically the UK) as residential and commercial door locks and on safes. Safe-deposit boxes in banks around the world use lever designs heavily.

History

One of the early lever lock designs was the Banbury lock created in the late 1700s. This design did not use fences and gates, but rather a simple hinged lever that the key had to lift out of the way in order for the bolt to retract. Security was provided by traditional keyway warding.

Barron lock

In 1778, Robert Barron patented the first lever lock that used a fence and gates. The levers utilized a technique called double action in order to provide increased security. This technique requires each lever be lifted to a precise height at which the fence can pass through the gate. Overlifting a lever causes it to block the fence; older locks' levers could just be lifted to any height as long as they cleared the obstacles. The double-acting lever principle is still in use to this day, and was also eventually applied to pin-tumbler locks by Linus Yale, Jr.

Chubb lock

The Chubb Detector lock.

In 1827, Charles and Jeremiah Chubb patented a lock design based on Barron's work. Their version reversed the placement of the fence and gates, attaching the fence to the bolt and the gates to the levers. This design still in use today in many locks. They also added a device called the detector, an extra lever that triggered by overlifting of the main levers. When triggered, the Detector would lock the bolt until it was reset with a special key. Chubb added serrations on the gate levers which prematurely bound components if tension was applied when the component was in the incorrect position. This design was also eventually included in security pins by many other lock designs. In 1883, Chubb patented a rotating barrel that closed off the keyway when the key was turned. This addition helped to prevent decoding.

Tucker and Reeves

In 1851, a new design surfaced with a bolt that was not rigidly fixed but could shift on one end. Patented by Tucker and Reeves, this design aimed to thwart picking attempts involving pressure on the bolt. The shifting bolt made it harder to feel the gates inside the lock as it shifted. In 1853, the design was refined to include a rotating barrel that prevented movement of the bolt until a key was inserted.

Parsons lock

In 1832, the Parsons lock was created. This design had seven symmetrical levers that pivoted around their midpoint (traditional levers were hinged at one endpoint). The key lifted the levers at one end and the bolt had notches at both ends. Overlifting any lever would cause it to engage the notch in the bolt and lock it at that end even if the other end had cleared the bolt.

Principles of Operation

A series of levers is placed in the lock. The entire set of levers must be properly raised by the key to allow a piece of metal connected to the bolt to pass through the gates of the levers, retracting or extending the bolt. Each lever may have a larger undersection or a different gate position to provide differs.

Components

Levers

The primary locking component of lever lock. Each lever is a flat piece of metal with a gate which must be raised to the proper position to allow the stump to pass through and retract or extend the bolt. Each lever is self-tensioned by a built in spring, sometimes referred to as the "fly". Some levers use a thinned belly section referred to as "conning" to ensure the lever interfaces with the correct bitting area on the key.

Stump, Fence

The stump, or fence, is a protrusion connected to the bolt. The stump prevents the bolt from being extended or retracted until the levers are properly positioned. Traditional designs have the stump and levers interconnected (gates are closed, with the stump sitting inside each lever).

Washers

Washers are flat metal plates placed between each lever to ensure that each lever is properly raised by each bitting cut. They are not universal, but common in outdoor facing lever locks that require a high degree of reliability, especially in harsh conditions.

Curtain

A curtain is a component used in the keyway to prevent direct access to the levers until the key is fully rotated in the lock. This protects against casual manipulation of the levers, but does not dissuade lockpicking attacks completely.

Vulnerabilities

Lever locks are vulnerable to a wide variety of attacks depending on their design. Tools to pick and decode lever locks are not as widely available as their pin-tumbler counterparts, but are equally prevelant and effective.

• Lockpicking
• Impressioning
• Decoding
• Bypass

Notes

• Lever locks are not subject to key bumping or pick gun attacks.

See also

• Lock
• Key
• Lockpicking