Interchangeable core

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An interchangeable core is a small, self-contained lock cylinder, usually “figure-eight” in shape, that can be extracted from its housing via a special “control key” and is designed to fit into a variety of cylinder housings that comply with its size specifications, either large or small format through standardization, and produced by a variety of lock manufacturers.

Interchangeable cores can be removed from one type of lock (bored cylindrical lock, mortise lock, padlock, etc.) and placed into another lock without removing or disassembling the lockset/door hardware. Interchangeable core lock systems were designed to permit the manager of the system to rekey the locks without possessing expertise. Most interchangeable lock systems come with spare cores to allow instant replacement in an emergency (such as a stolen key or personnel change) and maintain security. The old cores are either stored to be reused later or sent out for rekeying. Interchangeable core locks are readily adapted for master keying systems. A key retainer is often used to support visual key control within interchangeable core systems.

The interchangeable core was invented by Frank Best in 1912^[1]. Frank Best went on to found Best Universal Lock Company which eventually came to be Best Access Systems, Inc. The Best style of interchangeable core has become the most well known type of interchangeable core cylinder^{[citation needed]}, and is easily recognizable by the 'figure-8' shape of the core's face. This type of cylinder is also offered by many other commercial lock manufacturers such as Arrow, Falcon, Schlage, Ultra Security, Medeco, Lori, Yale, Kaba-Ilco, Scorpion and KSP, and is often referred to as a small format interchangeable core (SFIC).

Additionally, large format interchangeable core cylinders (LFIC) are also available from various other manufacturers, including Schlage, Medeco, Sargent, CorbinRusswin, Yale, ASSA, BiLock, Mul-T-Lock and Abloy. In most cases, they are larger in size than the SFIC, are designed to integrate with the manufacturers own keying system and differ in mechanical structure and operation between brands.

Although they're similar in appearance, different types can differ significantly in operation. The core removal on a Schlage LFIC is actuated by activating a control pin in the far end of the lock using any(usually the master) operating key cut onto a special control key blank with a long nose.

Best type SFIC has a separate shear line and operated by a control key with distinct bitting cut on an ordinary blank.

Both types have their own vulnerabilities. One thing that can be said for sure is that like master keying, the core interchange mechanism adds convenience at the expense of security.