K E Y O F T H E D A Y
This grouping includes traditional cylinders for both mortise and rim-mounted door hardware.
IC or Interchangeable Core cylinders, pioneered by Best Universal Lock Co., allow for real-time rekeying of doors, padlocks, drawers, etc.
Here are several Best 'cores', retired from government service, that can be removed from lock cylinders by using a properly bitted Control Key.
Cylinders and cores can be rekeyed, given the proper parts and talent. These are examples of rekeying supplies.
A good example of a Russwin keying kit.