A key track system for a filter base module comprises a ring-shaped fixture including a series of perforations, each perforation at least partially defining a parting line along which a tab may be selectively removed. The key track fixture is incorporated into the filter base module to define the periphery of an entryway to a cartridge-receiving receptacle in the header portion of a base module. In some embodiments, the key track fixture is a molded ring-like component with pre-key selected angularly spaced key slots. Base modules including the key track system may be efficiently configured to accept the key pattern of a filter cartridge compatible with the filter system in which the base module will be used.