A lock cylinder is a type of lock that is constructed with a cylinder, in order that a locksmith can easily unscrew the lock in case of rekeying. The cylinder can therefore contain a wide variety of locking mechanisms, including the wafer tumbler lock, the pin tumbler lock, and the disc tumbler lock.
Cylinder locks, also know as profile cylinder locks, have two main advantages. The first advantage is that they can be easily changed without affecting the hardware of the boltwork. In order to remove the cylinder, one need only loosen a set of screws, and then remove the cylinder from the separate boltwork. The second advantage is that one can buy cylinders in multiple different formats which can all be used with the same kind of key. Thus the user can have keyed-alike and master-keyed systems which accommodate many different kinds of lock, such as nightlatches, deadbolts and roller door locks. Padlocks can also be included, although is it rare for these to have removable cylinders.
Standard types of cylinder lock include key-in-knobset cylinders, rim - also known as nightlatch - cylinders, Ingersoll format cylinders, American and Scandinavian round mortise cylinders, and Scandinavian oval cylinders. Similarly, there are also standardised cross-sectional profiles lengths for cylinders, to suit different types of door thickness. These profiles include the europrofile (or DIN standard), the British oval profile and the Swiss profile.
Cruciform pin-tumbler locks can also use interchangeable cylinders, as do a few sophisticated lever locks.
Types of lock cylinders:
Individually keyed system (KD)
With an individually keyed system, each cylinder can be opened by a unique key.
Keyed alike (KA)
This system allows for a number of cylinders to be operated by one key. It is ideally suited to residential and commercial applications such as front and back doors.
Master keyed (MK)
With a master-keyed system, each lock has its own individual key which will not operate any other lock in the system, although all locks can be operated by a single master-key. This is usually applied in commercial environments.
Grand master keyed (GMK)
An extension of the master-keyed system whereby each lock has its own individual key with the locks being divided into two 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 suited to complex commercial systems.
Common entrance suite / Maison keying (CES)
This locking system is often used in apartments, office blocks and hotels. Each apartment or room has its own individual key which will not open the doors to any other spaces, but will open common entrance doors and communal service areas. It is often used in combination with a Master Keyed system in which the master key is kept by the landlord.
The one weakness of lock cylinders is that their weakness at the centre can be open to snapping. This risk can be overcome by purchasing an anti-snap cylinder, which leave the locking mechanism inside the door intact.