Skeleton Key
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A "lever lock" type key.

A skeleton key (Master key) is either a key that has been altered in such a way as to bypass the wards placed inside a warded lock, or an American term for a lever or 'bit' type key.

Warded locks

A keyhole.

A skeleton key is one that has been filed or cut so that it can be used to unlock a variety of warded locks each with a different configuration of wards. This can usually be done by removing most of the centre of the key allowing it to pass by the wards without interference unlocking or locking the lock. To counteract this wards were placed not just in the center but on the outside as well, making it harder for illegal attempts at making a key to be successful.

Lever lock keys

The term "skeleton key" is also often used to describe lever lock keys. This usage perhaps stems from such keys' resemblance to a skeletal figure, the lock's hole into which the key is inserted is fashioned in the shape of a circle at the top, with flared lines projecting down from it to form the sides of an isosceles triangle, the circle at the top then circumscribing the triangle at one-third the vertical length of the two sides resembling a stylized skull.

In the United Kingdom

Lever Lock skeleton keys or master keys as they are more commonly known are used in a lock with a combination of usually 5 or 3 levers and a set of wards that come into contact with the bit of the key only on the sides - the top is for pushing the levers to their correct heights while the warded section of the key just has to pass uninterrupted to allow the key to fully rotate. A master key system will have all the levers heights the same but each door will have different wards. A skeleton key has the warded section of the key removed so that it opens all the doors of a system. Not to be confused with a system where all the locks are keyed alike (one type of key will open all locks but each lock does not have its own unique key that will open only it).

In the U.S.

These keys were common in both cabinetry and door locks in early Colonial America and remained in common usage within the United States through the 1940s, giving way after World War II to the pin tumbler lock. Most skeleton keys and their locks were formed of brass, although pewter was sometimes used as well. Today, skeleton keys are associated with fine cabinetry. They are insecure locks, since they cannot be ground to unique shapes to form a unique key pattern.

See also

Look up Skeleton key in
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• Master key, another name for a skeleton key.