Thje Dupli-Key system utilizes two different sets of numbered key tags to make managing keys as efficient as possible. Attach your master keys to the red octagonal-shaped self-locking key tag to ensure the original is never loaned. Fasten duplicate loaner keys to white oval-shaped, snap-hook key rings and file them on the same hook as the master. When a loaner key is issued, insert a receipt slip in the brass holder and place on hook. Keep track of all vital key information in the Cross Reference Index Kit (included).