- Interchangeable cores have three shear lines, which is why they carry more pins and pick more easily.
- The control key removes every core in the building. Issue one and log every copy.
- Small format is the figure eight shape and is broadly cross compatible. Large format is not.
- Keep rotating core stock so a rekey becomes a swap done under shop conditions.
How the control key works
A small format interchangeable core has three shear lines rather than one. The operating shear line lets the change key turn the plug and throw the bolt. The control shear line, set higher, lets the control key rotate a lug that retracts the core's retaining fin so the whole core slides out of the housing.
That means every core needs an extra build pin in every chamber, which is why interchangeable cores carry more pins and are less pick resistant than an equivalent conventional cylinder. It is a deliberate trade of security for administrative speed.
Control keys must be treated as the most sensitive key in the building. Anyone holding one can remove every core, take them away, decode them at leisure and return them. Issue control keys to one named person and record every copy.
Small format and large format
Small format interchangeable core is a figure eight shape originating with Best and now made by many manufacturers, largely cross compatible. Large format interchangeable core is a manufacturer specific round core used by brands such as Schlage and Corbin Russwin, and it is generally not cross compatible.
Before quoting a job identify which the building uses, because a box of the wrong cores is money spent and time lost. The figure eight face is unmistakable once you have seen it.
Stock a set of blank cores and a pinning kit. The value proposition of interchangeable cores is that a tenant change becomes a five minute visit. If you have to order cores each time, the customer loses the only benefit they paid for.
Running a core exchange program
The professional way to service an interchangeable core building is to keep a rotating stock. Pin new cores in the shop, carry them to site, swap them out and bring the removed cores back to be repinned for the next rotation.
That turns an on site rekeying job into a swap, which means the work happens under shop conditions with a full pin kit rather than crouched in a corridor. It also means a lost key emergency can be answered in minutes.
Charge for the program rather than for the visit. A monthly or annual key control agreement with a defined number of core changes is recurring revenue, and it is the type of contract that makes commercial work more stable than residential work.
Common Questions
What makes an interchangeable core worth the extra cost?
Rekeying a door becomes a ten second job with no tools. On a site with staff turnover that pays for itself the first time somebody leaves without handing a key back.
What is a control key?
The key that lifts a core out of its housing. Whoever holds it can rekey the whole site, so it belongs in a safe and not on the maintenance ring.
Small format or large format?
Small format is the common six or seven pin figure eight core. Large format holds more pins and more levels of masterkeying. Pick one and stay with it, because they do not mix.