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Advanced Locksmith Lesson 1 How Interchangeable Core (IC) Locks Work.
Interchangeable core definition from Wikipedia

"An interchangeable core or ic is a compact keying mechanism in a specific "small format" figure-eight shape. Unlike a standard key cylinder, which is accessible for combinating only via locking device disassembly, an interchangeable mechanism relies upon a specialized "control" key for insertion and extraction of the essential (or "core") combinating components."
That is the formal definition. Here is the simple definition. It it a lock core that can be install or removed from the locks housing with a control key. IC core locks have been around for a long time, Frank Best first patented the IC core idea in 1923.

Interchangeable or removable cores are a great tool for locksmiths, property managers and landlords. They allow you to easily and quickly change the lock without disassembling the lock. All you have to do is insert the control key, turn it, then pull the lock cylinder out. Next insert you control key into the new cylinder, turn it, insert the core into the lock housing, turn the key in the opposite direction, remove the key and you are done. It is so easy a child could do it.

Some uses of IC car locks are in padlocks, file cabinets, medical cart locks, cam locks, desk locks, drawer locks, and key switches. There are over 2 billion cores in use all over the world. These locks are also harder to by-pass (pick) which increases security.
There are many different types of IC cores. The most popular is the Small Format Interchangeable Core (SFIC) A/2 system. There are 3 SFIC systems A/2, A/3, and A/4.A/2 is the most common, A/3 is not used very widely and A/4 in institutional locksmithting (i.e. schools and government buildings). There are also large format IC core locks. They are not interchangeable with SFIC locks. They are used in many of the same applications but the lock cylinder is larger than the SFIC core cylinder.
There are 2 main types of keys. The user key (operates the lock to open it) and control key ( used to remove/change the core) . The control key uses the same key and the user key, it is just cut to different bittings. SFIC cores can be master keyed just like any other lock as long as you follow the rules for pin combinations. You can also master key the control key.

This is a great article on IC core locks .  Click here to download it.

IC core locks are a little bit more challenging to re-key. We will cover re-keying them in the next advanced lesson.

If you are comfortable whit the material above then it is time to move on to the next lesson. Click here to go to the next lesson.