Control keys in a Small Format Interchangeable Core (SFIC) system are just like the other system keys, but are cut to work the upper shear line. A shear line is where all the pins must line up in order for the key to turn. A standard cylinder has 1 shear line that operates the lock, but a Small Format core has 2 shear lines; 1 that operates the lock, and 1 that retracts the control lug releasing the core.
If you don't have a control key there are still options for you. There are a few techniques to remove SFIC cores without control keys, but there are no do-it-yourself options. A core must be removed and decoded, then a control key can be cut with the information that should remove the remaining cores in your system. A core can be picked to control to remove the core, but it is difficult. Another option is to drill the core, but it must be done carefully to preserve the pin stacks and not damage the lock. If the pin stacks are damaged you lose the information to cut cut a control key for the remaining cores.
Most locksmiths should be able to do this for you, but it would be a good idea to call first and ask them if they can. The problem today is that many locksmiths don't do anything except rekey locks and open cars, so if you get someone who sounds unsure you may want to keep looking. If you are able to remove a lock that is not essential for a few hours you could probably save a service call by bringing the lock to them.
If you don't have a locksmith skilled in SFIC locally, we may be able to help. If you have a lock that is not essential, and have the ability to send us the part that has the core in it, we will decode it and cut you a control key for the remaining cores in your system. Just keep in mind that it is being done through the mail, so make sure that you won't need the lock for a week or so.
As always if you have any questions feel free to call us. There is never a charge for consultation, even if we are referring you to someone else.
SFIC Security Solutions