Key relevance
Encyclopedia
In master locksmithing
Locksmithing
Locksmithing began as the science and art of making and defeating locks. A lock is a mechanism that secures buildings, rooms, cabinets, objects, or other storage facilities. A key is often used to open a lock...

, key relevance is the measurable difference between an original key
Key (lock)
A key is an instrument that is used to operate a lock. A typical key consists of two parts: the blade, which slides into the keyway of the lock and distinguishes between different keys, and the bow, which is left protruding so that torque can be applied by the user. The blade is usually intended to...

 and a copy made of that key, either from a wax impression or directly from the original, and how similar the two keys are in size and shape. It can also refer to the measurable difference between a key and the size required to fit and operate the keyway
Keyway
A keyway is the shaped channel in a lock cylinder into which the key slides to gain access to the lock tumblers. Lock keyway shapes vary widely with lock manufacturer, and many manufacturers have a number of unique profiles requiring a specifically milled key blank to engage the lock's...

 of its paired lock
Lock (device)
A lock is a mechanical or electronic fastening device that is released by a physical object or secret information , or combination of more than one of these....

.

No two copies of keys are exactly the same, unless they were both made from key blanks
Key blank
A key blank is a key that has not been cut to a specific bitting. The blank has a specific cross-sectional profile to match the keyway in a corresponding lock cylinder. Key blanks can be stamped with a manufacturer name, end-user logo or with a phrase, the most commonly seen being 'Do not duplicate'...

 that are struck from the same mould or cut from the same duplicating/milling machine
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

 with no changes to the bitting
Bitting
A bitting is the part of the key that actually engages the tumblers to activate the lock. Bittings are often represented as a code which instructs how a key is to be cut by a locksmith. The bitting is usually a series of integers that is usually translated from a key code chart or from a...

 settings in between. Even under these favorable circumstances, there will be minute differences between the two key shapes, though their key relevance is extremely high.

In all machining work, there are measurable amounts of difference between the design specification of an object, and its actual manufactured size. In locksmithing, the allowable tolerance is decided by the range of minute differences between a key's size and shape in comparison to the size and shape required to turn the tumblers within the lock. Key relevance is the measure of similarity between the key and the optimal size needed to fit the lock, or it is the similarity between a duplicate key and the original it is seeking to replicate.

Key relevance cannot be deduced from a key code
Key code
A key code is a series of alphanumeric characters used by locksmiths to create a key. There are two kinds of key codes: blind codes and bitting codes.-Blind codes:...

, since the key code merely refers to a central authoritative source for designed shapes and sizes of keys.

Typical modern keys require a key relevance of approximately 0.03 millimetre (0.00118110236220472 in) to 0.07 millimetre (0.00275590551181102 in) (accuracy within 0.75% to 1.75%) in order to operate.

Other applications

"Key relevance" may also be applied to types of electronic lock
Electronic lock
An electronic lock is a locking device which operates by means of electric current. Electric locks are sometimes stand-alone with an electronic control assembly mounted directly to the lock. More often electric locks are connected to an access control system...

s when used to refer to similarities in magnetic signatures or radio code
Radio code
Radio codes include:*ICAO spelling alphabet*Ten-code*Procedure word*Voice procedure*Q code*Morse codeAlso see encoding generally....

s, though truly digital-coded radio signals do not have key relevance ratings because they must have precise unlocking codes, with no degree of difference whatsoever in order to operate.

The term has also occasionally been co-opted by broader mechanical engineering
Mechanical engineering
Mechanical engineering is a discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the production and usage of heat and mechanical power for the...

 to refer to the similarity of fit between two interlocking machined parts, although "tolerance" or "backlash"
Backlash (engineering)
In mechanical engineering, backlash, sometimes called lash or play, is clearance between mating components, sometimes described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established...

 has gained far wider adoption and acceptance in usage.

See also

  • Margin of error
    Margin of error
    The margin of error is a statistic expressing the amount of random sampling error in a survey's results. The larger the margin of error, the less faith one should have that the poll's reported results are close to the "true" figures; that is, the figures for the whole population...

  • Process capability
    Process capability
    A process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts...

  • Specification
    Specification (technical standard)
    A specification is an explicit set of requirements to be satisfied by a material, product, or service. Should a material, product or service fail to meet one or more of the applicable specifications, it may be referred to as being out of specification;the abbreviation OOS may also be used...

  • Engineering tolerance
  • Tolerance stacks
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