How do ABC cylinders work?

Some of our doors come supplied with a cylinder and a set of ABC keys:

A – Fitters keys (these have a blue cover on them) – You can give to your builder when installing your door and allow for normal operation of the door lock during the fitting process.

B – Master key (can be a silver key with no covers, or key with a slot taken out of the end). This key is the main key for the door and allows you to void the use of the fitters keys if required. Once you insert and rotate the key on the pull side of the door (side where the hinges are visible), it removes a ball bearing and stops the fitters keys from working. It can still be used for everyday use if needed.

C – Remaining usable keys (these have a black cover on them) – These are your keys for normal everyday use and come in a sealed packet with the master key. These keys are not voided when the master key has been used.