Abstract: A keyblock is shown for use in a computer cage having an interior and a guide rail for guiding a logic-card book into position within the interior. The keyblock is installed within a cage guide opening provided at an end of the guide rail within the cage interior by means of a downwardly projecting dart which is received within the opening in snap-fit fashion. Locating pins on the keyblock lower surface properly position and align the keyblock within the cage guide opening. Contoured regions on the keyblock upper surface engage and lead-in a complimentary surface located on the logic-card book being received within the cage interior. One or more slots provided between selected contoured regions provide a coded pattern which matches a pattern provided on the desired logic-card book to be received in a predetermined position within the cage interior.