What are Interchangeable Cores?

OpenLocks Team

Interchangeable cores (IC) are a convenient way to be able to switch out locks without having to dismantle the entire door handle or lockset. They allow someone with a special key called the “control key” to quickly remove the lock and replace it with another one.
Interchangeable Core being removed by Control KeyBecause they can be changed so quickly, Interchangeable cores are frequently used in large commercial, institutional and residential settings. If a tenant moves out, or wants to change their locks, the superintendent or facilities manager can easily remove their locks and put in new ones. Contrast this with standard locks, which require dismantling the door in order to change the locks which could take up to hours per lock, it saves a lot of time especially in buildings with dozens of doors.
The way that it works is the control key. The control key is a special key, which doesn’t actually open the door at all. Its only purpose is to remove the interchangeable core so that it can be rekeyed or replaced. A simple turn releases the core from the housing, which is the interface between the core and the door. When an interchangeable core is inserted into a housing, it is mechanically locked into place and cannot be removed except by using the control key.
Housing for Interchangeable Core Showing MechanismIf you are considering using interchangeable cores for your project, bear in mind that there are two components (which can be purchased together): the core itself, and the housing for it to be inserted to. The housing is the part which is installed into the door hardware, The housing is the piece which interacts with the door and actually causes the latch to turn. It’s made of a single piece of metal, with a ‘cam’ or tail at the back which turns the lock. Housings made for interchangeable cores have figure-8 shaped opening in the front, for the core to be inserted into. Without the core, a housing is useless as a lock and the door can be opened with a simple screwdriver as you can see in the image to the right.
Those are the basics, but of course with anything lock-related, things get complicated when you start to get specific about the brand of lock that you want. Interchangeable cores were invented by Best Access Systems back in the day and since then everyone has jumped on board. They’re just so convenient, all the lock makers wanted a piece of the pie: Schlage, Corbin-Russwin, Ilco, Yale, Arrow, and so on. 
Brands of Interchangeable CoreWhile most of the interchangeable cores are standardized, some of the brands also have their own sizes. In most cases, you’re going to want a Small Format Interchangeable Core (SFIC). That’s the standard size, which you can switch out with practically any other brand in the future. Only if you really need it for a specific reason should you order Full Size Interchangeable Cores (FSIC). The sizes and shapes of FSIC are specific to each brand. Sometimes, buildings have a standard lock they use, and they require FSIC cores.
If possible, your best option is to request your door vendor to provide housings to accept Small Format Interchangeable Cores, which they can pre-install so when the job’s done you can simply go around and put in the cores with the control key. In some cases the core can be installed directly into the handle without a housing, which is even easier. 
If that’s not possible, you will need to order the housings yourself, which is not too hard. You just need to know two things: First, is the door using a locking pull or a mortise lockset? Pulls will need a Rim Housing, which has a long tail on the end to pass through the pull to the thumb turn on the inside. Second, if you have a mortise lockset, you’ll need to know which type of cam to use for the Mortise Housing. This really depends on the brand of lockset that you have. There are a few different common types, and an easy rule of thumb is to order the cam from the same brand as your lockset.
If Interchangeable Cores still leave you scratching your head, leave your question in the comments or email us at, we’ll be glad to answer it. 

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