core n. a complete unit, often with a “figure eight” shape, which usually consists of the plug, shell, tumblers, springs, plug retainer and spring cover(s). It is primarily used in removable and interchangeable core cylinders and locks.

Examples of cores.

Examples of cores.

Cores are very much like cylinders in that they are both complete operating units, containing a plug, shell, tumblers, springs, a plug retainer, and spring covers. Unlike cylinders, however, cores generally do not have a cam or tailpiece directly attached to them, although there are rare exceptions. Also unlike cylinders, cores are inserted either directly inserted into the lock, such as in the handle of a leverset, or into housings rather than screwed in or via use of a spring loaded, retaining pin.

housing n. that part of a locking device which is designed to hold a core

Examples of housings.

Examples of housings.

Housings are frequently described as either rim or mortise. Rim housings utilize tailpieces and interface with surface mounted hardware. Mortise housings utilize cams and interface with mortise locks.

The primary benefit of cores, as opposed to cylinders, is that they allow the user to remove the core from the lock or it’s housing by using a control key.

control key n. 1. a key whose only purpose is to remove and/or install an interchangeable or removable core 2. a bypass key used to operate and/or reset some combination type locks 3. a key which allows disassembly of some removable cylinder locks

A control key works by retracting the control lug, which then allows the core to be removed from either the lock or it’s housing.

control lug n. that part of an interchangeable or removable core-retaining device which locks the core into its housing

Control lugs on interchangeable cores.

Control lugs on interchangeable cores.

Control lugs are generally found above the core’s plug although different designs can place them elsewhere. A manufacturer’s design ultimately dictates the position and function of the control lug. Control keys either directly manipulate the control lug, such as lifting a special pin to engage it, or form a separate shearline to retract the control lug.

Core Types

There are two types of cores: removable cores and interchangeable cores.

removable core n. a key removable core which can only be installed in one type of cylinder housing; e.g., rim cylinder or mortise cylinder or key-in-knob lock

Sargent "Old Style" removable cores.

Sargent “Old Style” removable cores.

Sargent "Old Style" removable cores. Note the differences at the back of each core.

Sargent “Old Style” removable cores. Note the differences at the back of each core.

Perhaps the best examples of removable cores are the Sargent’s “Old Style” cores as well as their Keso/Keso F1 cores.

interchangeable core n. a key removable core which can be used in all or most of the core manufacturer’s product line. No tools (other than the control key) are required for removal of the core.

Examples of interchangeable cores.

Examples of interchangeable cores.

Popular examples of interchangeable cores include small format interchangeable cores, such as those manufactured by Best and Falcon.

A majority of the cores you are likely to encounter will be interchangeable cores. Whereas removable cores require specific housings for specific cores, interchangeable cores can be utilized in virtually all housings across a manufacturer’s product line. For example, if I wanted to move an interchangeable core from a rim housing into a mortise housing I could do so without changing any of the the hardware.

Interchangeable Core Types

There are two types of interchangeable cores: small format interchangeable cores and large format interchangeable cores.

Small Format Interchangeable Core n. an IC that replicates the functionality and design popularized by Best

Examples of small format interchangeable cores.

Examples of small format interchangeable cores.

You’ll often hear this type of core described as a “Best Core” or “I-Core” or , worst yet, “IC Core”. The latter term, “IC Core”, perhaps grind my gears more than anything in this industry because literally translated it means “Interchangeable Core Core”. Small format interchangeable core is a bit lengthy I’ll admit but in our shop, and many others across the nation, we simply use the abbreviation for it: SFIC.

SFIC abb. Small Format Interchangeable Core

Every other interchangeable core form factor is referred to as a large format interchangeable core.

Large Format Interchangeable Core n. an interchangeable core which is too large to fit into a small format interchangeable core housing

Examples of large format interchangeable cores.

Examples of large format interchangeable cores.

A number of manufacturers have produced their own version of interchangeable cores. These manufacturers include Corbin Russwin, Medeco, Sargent, Schlage, Yale. Like small format interchangeable cores, large format interchangeable cores can be abbreviated.

LFIC abb. Large Format Interchangeable Core

When describing a type of LFIC, the manufacturer’s name usually precedes the LFIC abbreviation. For example, if describing a core type for a job, most locksmiths will typically say “Corbin Russwin LFIC” or “Yale LFIC”.

One important note is that Schlage doesn’t refer to their large format interchangeable cores as LFICs. To Schlage, their large format interchangeable cores are known as FSIC, or full size interchangeable core. Since the LIST Council hasn’t recognized this term/definition yet, I will refrain from officially recognizing it. That said, for many years Schlage’s large format interchangeable core was simply referred to as Schlage LFIC and many still refer to it as that, present company included.