Interchangeable Core Basics

Aug. 1, 2007
Use bottom pins that are manufactured of the same material as the original equipment keys. For example, use Brass pins with brass keys

The Best®/Falcon® type Figure “8” small format interchangeable core lock mechanism was developed so non-locksmith personnel could conveniently and inexpensively rekey a lock without any knowledge of how locks operate or how to service them. This concept, first patented by Frank Best in the early 1900s, still satisfies the needs of commercial and institution facilities that have a high rate of employee turnover.

The basic premise of the interchangeable core system is that the core is secured into the lock housing (I. E. mortise/rim cylinder, lever, padlock, etc.) by a sleeve-based lug. A control key is specially cut key whose function is to operate the control shear line that is between the sleeve and the housing. The properly control key rotates 15 degrees clockwise retracting the lug into the housing, permitting the core to be removed and inserted. Once the core has been removed, the combination can be changed or a different core inserted. The control key is designed only to remove the core, not to operate the lock.

Interchangeable cores make use of .108” diameter pins, seven thousandths of an inch smaller in diameter than the standard .115” diameter pins. Each pin chamber in an interchangeable core will contain three or four pin tumblers. A master keyed pin chamber will have four pin tumblers, unless the space position uses a constant. The four pin tumblers are a bottom pin, master pin, build-up (control) pin, and a top pin.

There are three distinct type/shape bottom pins for conventional interchangeable cores. Each offers specific functionality. For example, many institutional locksmiths who use Best cores want to only use the related Best components. One of the reasons is the Best core makes a distinctive “click” when the key is rotated. A second feature is there is little or no key “free play” in a Best core when operating it with a key cut to the Best specifications. Once the key is inserted, the tolerances are such that the key will not slide back and forth. The Best pinning configuration removes almost all of the lateral tolerances.

Best original bottom pins are made of nickel silver material, having a relatively thin chamber (.0055” +/- .0025”) on the top and straight edged angle towards the large diameter flat nose. I used a comparator to determine the shape and dimensions of several Best original bottom pins. My results were comparable for all of the pins I examined. The pin nose has an 84-degree included angle and ends with a .037” diameter flat nose.

LAB manufacturers bottom pins for use in Best interchangeable cores. They are sold under the LAB Brand IC Pins for use in Best Cores. The pins are manufactured of nickel silver material. The chamfer .0055” +/- .0025” on the top of the bottom pin has a straight edged angle towards a large diameter flat nose. The comparator was used and the results for the LAB bottom pin nose has an approximate 84-degree included angle that ends with .037” diameter flat nose.

The Best keys that I examined were manufactured from nickel silver material, having a .045” flat and an angle of cut that is 90 degrees. The large pin nose and the relatively small flat do not leave much room for inaccurate key cutting.

Other brands of interchangeable cores use different shape nickel silver bottom pins. These nickel silver material pins have a thicker chamfer .008” +/-.002” on the top and rounded angles towards the nose with a much smaller diameter, somewhat rounded nose .0225” +/- .0025”. The included angle was 90 degrees with a somewhat flat nose of .015”+/-.005” diameter.

Interestingly, different IC core manufacturers can have varying dimensions for the included angle of cut and the size of their flat even though they use the standard space and depth dimensions.

LAB has a Universal interchangeable core bottom pin design. This Universal design bottom pin is manufactured of full hard brass material. The chamfer .012” +/- .001” is thicker with a straight edged angle towards a smaller rounded nose. The included angle is 90 degrees with the nose .022” +/- .003”. The Lab Universal interchangeable core bottom pins are color coded to exact industry standards.

LAB Security Executive Vice President Jerry Roraback strongly suggests that before purchasing replacement pins for interchangeable cores, make sure you know whose cores you are repinning and the key blanks material. If you are using a nickel silver key blank and the cores are BEST, only re-pin with the BEST tumbler pin design. If your cores are not BEST but use nickel silver key blanks, use what LAB refers to in its product line as “LAB Original I. Core Pins” (for use in interchangeable cores: Falcon, Schlage Small format, Medeco Keymark, etc.) When repinning interchangeable cores with a brass key, LAB's color coded .108 diameter interchangeable core pins will function well.

Why the different bottom pin material? Lock manufacturers strongly recommend using bottom pins that are manufactured of the same material as the original equipment keys. Brass pins should be used with brass keys and nickel silver pins should be used with nickel silver bottom pins. Similar materials will cause even wear on both edges, whereas dissimilar materials will over time result in uneven wear on the softer metal object.

This leads to the cutting of interchangeable core keys. Interchangeable Core keys are cut to very tight tolerances. This is because there are only .0125” increments, smaller diameter pins and the cores are also made to tight tolerances.

When cutting interchangeable core keys, these tip stop keys are difficult to properly align. The Schlage SFIC uses a shoulder stop key. The blade is also thin and usually of paracentric design. As a result, the keyway has to be thinner because of the sectional applications. In addition, there are many different keyways.

This results in difficulty holding the key blank in position within a key machine key vise. One method of securing the key and key blank is to use paper clips and different pieces of wood or metal to better position the key and key blank blades for duplication and/or origination.

Rytan, a key machine manufacturer, has introduced Key Adapters that secure the specific keyway key blades in the proper position without distortion, when duplicating. The Key Adapters are designed to operate with most cylindrical key duplicating machines.

Without some type of assistance, what can and does often happen is the blade becomes distorted without the locksmith even knowing this problem is occuring. The distortion causes the cuts to be either too shallow or too deep and somewhat out of position. When the cut key is removed from the vise jaw, the blade straightens out somewhat changing the cut geometry.

This is why most interchangeable core manufacturers strongly recommend using punch style key machines to cut their IC keys. This way each key is an original rather than a duplicate.

For more information on interchangeable cores, contact your local locksmith wholesaler or:

Arrow Lock, Telephone: 800-839-3157 Fax 800-421-6615. Web site:

Corbin Russwin, 225 Episcopal Rd., Berlin , CT 06037 . Telephone: 704-283-2101. Fax: 800-447-6714. Web Site:

Falcon Lock Co., 2315 Briargate Pkwy #700 , Colorado Springs , CO 80920 . Telephone: 800-266-4456. Web site:

LAB Security, 700 Emmett Street , Bristol , CT 06010 . Telephone: 860-589-6037. Fax: 860-583-7838. Web site:

Medeco Security Locks, 3625 Allegheny Dr , Salem , VA 24153 . Telephone: 800-675-7558. Fax: 800-421-6615. Web Site:

SARGENT Lock, 100 Sargent Drive , New Haven , CT 06511 . Telephone: 800-727-5477. Fax: 203-821-5793. Web site:

Schlage, 111 Congressional Blvd., Suite 200 , Carmel , IN 46032 . Telephone: 800-847-1864. Web Site:

Yale Commercial Locks and Hardware, 100 Yale Avenue , Lenoir City , TN 37771 . Telephone: 704-283-2101. Fax: 800-338-0965 Web Site:

For more information on key adapters, contact your local locksmith wholesaler or Rytan, Inc., 455 Maple Avenue , Torrance , CA 90503 . Telephone: 800-447-9826. Web site: