Interchangeable Core Basics

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.