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A cylinder lock is a lock constructed with a cylinder that a locksmith can easily unscrew to facilitate rekeying. The cylinder may contain any of a variety of locking mechanisms, including the pin tumbler lock, the wafer tumbler lock and the disc tumbler lock.
The first main advantage to a cylinder lock, also known as a profile cylinder lock, is that the cylinder may be changed without altering the boltwork hardware. Removing the cylinder typically requires only loosening a set screw, then sliding the cylinder from the boltwork. The second is that it is usually possible to obtain, from various lock manufacturers, cylinders in different formats that can all be used with the same type of key. This allows the user to have keyed-alike, and master-keyed systems that incorporate a wide variety of different types of lock, such as nightlatches, deadbolts and roller door locks. Typically, padlocks can also be included, although these rarely have removable cylinders.
Standardised types of cylinder include key-in-knobset cylinders, rim (also known as nightlatch) cylinders, Ingersoll format cylinders, American, and Scandinavian round mortise cylinders, and Scandinavian oval cylinders. There are also standardised cross-sectional profiles for lock cylinders that may vary in length - for example to suit different door thicknesses. These profiles include the europrofile (or DIN standard), the British oval profile and the Swiss profile.
Types of cylinder locks
Cruciform pin-tumbler locks may also use interchangeable cylinders, as do a few sophisticated lever locks.
- Individually keyed system (KD)
With an individually keyed system, each cylinder can be opened by its unique key.
- Keyed alike (KA)
This system allows for a number of cylinders to be operated by the same key. It is ideally suited to residential and commercial applications such as front and back doors.
- Master keyed (MK)
A master-keyed system involves each lock having its own individual key which will not operate any other lock in the system, but where all locks can be operated by a single master-key. This is usually applied in commercial environments.
- Grand master keyed (GMK)
This is an extension of the master-keyed system where each lock has its own individual key and the locks are divided into 2 or more groups. Each lock group is operated by a master-key and the entire system is operated by one grand master-key. This is ideally utilized in complex commercial systems.
- Common entrance suite / Maison keying (CES)
This system is widely used in apartments, office blocks and hotels. Each apartment (for example) has its own individual key which will not open the doors to any other apartments, but will open common entrance doors and communal service areas. It is often combined with a Master Keyed system in which said key is kept by the landlord.
Cylinder locks are vulnerable to a technique known as "lock snapping", also known as "cylinder snapping", where force is applied to the lock until it breaks into two pieces. The attack exploits the fact that a double cylinder lock is inherently weak in the centre. The attack typically takes between 50 seconds and 2 minutes. In February 2012 West Yorkshire Police revealed that 27% of all burglaries in the county used this technique.
To overcome the risk of "lock snapping", several lock manufacturers have developed higher security anti-snap cylinders. These security cylinders typically feature anti-snap lines and are British Standard Kitemark, Sold Secure Diamond rated and Secured by Design approved. The anti-snap lines act as sacrificial points, meaning that if force is applied to either end of the cylinder it will break away only to the anti-snap line, leaving the mechanism inside the door intact—allowing the correct key to still operate the lock.
Pin and tumbler cylinder locks are vulnerable to picking. This technique involves a pick, which is a thin piece of hard steel with a small diamond shape at its end. A tension wrench is inserted into the keyway alongside the pick and used to rotate the cylinder. The technique relies on small imperfections in the cylinder, that lead to a single pin holding the cylinder from rotating. The burglar applies constant (though weak) torque on the tension wrench inserted into the cylinder, and tries the pick at each pin. When the pick fiddles with the pin that actually holds the cylinder, the cylinder will rotate minutely, until another pin will stop it. Now the first pin is held above the shear line by the cylinder itself, and the burglar can proceed to pick the other pins. Though these principles are easy to understand, in practice a great deal of experience and patience is required in order to master this technique. Very high quality cylinders are less prone to this attack, requiring more time as well as superior skill.
A similar concept is utilized in powered picks. These appliances require no skill to operate, but are noisy so their usefulness for criminal use is limited. The powered pick uses multiple picks simultaneously, which are bounced very rapidly, and within minutes a common cylinder yields.
- Practical Course in Modern Locksmithing. Nelson-Hall Publishing Company. 1943. ISBN 0-911012-06-0.
- "Rise in 'lock snapping' burglaries in West Yorkshire". BBC News. 2012-02-20.