Servicing the Yale Large Format Interchangeable Core

Sept. 1, 2008

The Interchangeable Core (IC) lock mechanism was developed as a simpler way to rekey locking hardware without removing the entire lockset/cylinder from the door. Interchangeable core lock mechanisms can be used with any type of lock hardware including cylindrical locks, mortise locks and exit devices.

Interchangeable core lock mechanisms use two types of keys, an operating key and a control key. The operating key is any key cut to accommodate the pin tumbler’s bitting configuration(s). The control key is used to remove and install the lock mechanism (core) from/into the lock hardware. A replacement core that uses a different operating key can then be installed, making the previous operating key inoperable. Once the interchangeable core had been removed, it can be combinated to a different bitting configuration.

The lock mechanism, the pin tumblers and any secondary components are contained within the body of the core. Since the introduction of the interchangeable core lock mechanism in the 1920s, numerous types and styles of interchangeable core lock mechanisms have been introduced.

Yale introduced its large format interchangeable core (LFIC) system during the early 1960s. The design incorporated the 0.51” diameter conventional lock cylinder plug and a standard single shear line housing. To control removal and insertion of the core, Yale extended the core’s overall length and located a control lug towards the rear of the housing. The control lug is a flat plate that extends out from the left side of the housing when no control key is operating the core. To remove the core from a cylinder or housing, the control lug must be retracted into the housing. To control the control lug, Yale added an additional space to the rear of the core. This space contains the special tumbler switch requiring a number one depth of cut to operate it.

In order to retract and to extend the control lug, the control key must have one tumbler length longer blade than the operating key. In addition, since the core has only one shear line, the control key must be cut to an operating key bitting in order to clear the shear line and permit the plug to rotate. Yale set the depth of cut required to operate the special tumbler switch at a number one.
When a proper length, properly cut control key with a number one tip cut is inserted, this key can turn approximately 20 degrees clockwise, retracting the control lug into the body of the housing. With the control lug retracted, a Yale LFIC can be removed or inserted.

Important: Yale LFIC cores will not fit into Best®/Falcon® style small format interchangeable core housings.

This design enables Yale to combinate these cores using the same pin tumblers (.115” in diameter) in the same configuration as their conventional lock cylinders. This is extremely practical as the same Yale keys can operate both Yale conventional lock cylinders and the Yale LFIC lock cylinders. These cores use standard size pin tumblers. There are no build-up pins or control pins used to combinate a Yale large format interchangeable core.
The control lug is towards the rear of the core operated by a key with the same depths as the operating (or master key); only the blade is one pin length longer. For five-pin tumbler locks, the control key has six depths of cut. Five spaces are combinated for the lock mechanism. For six-pin tumbler locks, the control key has seven depths of cut. The cut closest to the tip must have a #1 depth in order to operate the control lug in either the five- or six-pin tumbler cores.

Note: When combinating a Yale large format interchangeable core, the depth of cut in the pin chamber adjacent to the tip cut must have a depth of cut that is within Maximum Adjacent Cut Specifications to the number one depth of cut at the tip.

A control key can be constructed from an operating key by using a control key blank that is one pin chamber longer than the operating key. Duplicate or originate the cuts onto this control key blank. The tip cut of a Yale original control key blank will have a number one depth of cut in the tip. In a master keyed system, the higher the level of the operating key (change, MK, GMK, etc.), the more cores the new control key will operate.
In the late 1990s, Yale changed the cutter angle and the flat (the dimension at the base of each cut) to a 95-degree included cutter angle and a .054” flat (the maximum length of the surface onto which each bottom rests. As a result the Maximum Adjacent Cut Specification (MACS) of the Yale Large Format Interchangeable Core, model 1210/1220 Series is five when using .019” pin sizes and four when using .025” pin sizes.

Two pin increment specifications are used by the Yale LFIC, the .019” and the .025”. The .025” pin increment specification is no longer used for new projects, only for existing projects. The .019” pin increment specification has a MACS of five, enabling up to a six depth bottom pin to be positioned a number one depth.

The .019” pin increment specification .115” diameter pin lengths are shown in Chart 1.
To simplify key identification, the Yale Large Format Interchangeable Cores use keys with two styles of bows. The “R” bow, a round head shape, is used as the operating (change and master) keys and the “F” bow, a diamond head shape, is used as the control keys. The “R” bow factory key blanks are available in six- and seven-pin tumbler. The “F” bow key blanks are available in seven- and eight-pin tumbler with the control key blanks having “0” cuts except for #1 cut (Tip Cut). “F” bow key blanks are stamped with word “Control”. Yale original key blanks are nickel silver.

The Yale LFIC cores are available with all of the Yale large pin tumbler keyways including the Standard Simplex, Simplex and the Surety. The Surety Keyways (multiplex keyways) use a variety of different shaped keyways that does not permit key interchange. Only the master key sections are milled to pass all the different keyways of a particular series.

For approximately 40 years, the Yale Large Format Interchangeable Core did not have top load capability for the pin tumblers. Starting in January 2002, Yale changed the design to incorporate a spring retainer slot and top loading capability into this Large Format Interchangeable Core. All Yale LFIC cores produced after this date are top loaded.

Note: For locksmiths rekeying Yale LFICs that do not have a spring retainer, the plug must be removed and the springs and top pins are loaded from within the plug housing.

When loading a combinated plug, use a setup key. A setup key operates as a handle to easily insert the combinated plug into a housing at an angle in order to not align the pin chambers. Once inserted, the plug can be rotated to align the pin chambers and remove the setup key.

The setup key is a key that has the correct blade length with each of the spaces cut to the deepest depth. A number nine depth of cut is specified for the Yale .019” pin increment specification. This way, whatever depth of cut a pin chamber has been combinated, both the bottom pin and the master pin (if equipped) will remain within the body of the plug.

The Yale Large Format Interchangeable Core mechanisms are available as conventional, security and patented keyway security in six- and seven-pin tumbler configurations. Note: For existing systems that use a five-pin tumbler configuration, do not combinate the sixth pin chamber.

The Yale LFIC cores are the same dimensions as the Medeco 31 Series cores. These cores can be used in Yale, Medeco and some Simplex locks equipped with the large format interchange core housings.

For more information, contact your local locksmith distributor or Yale, web site