Abstract: In a high speed impact printer having means for receiving a ribbon cartridge and for driving the ribbon in said cartridge, the improved apparatus comprising a ribbon cartridge to be inserted in said receiving means and adapted to be reversed one time only which comprises a cartridge housing with first and second reels rotatably mounted in said housing; each of the reels is adapted to support a portion of inventory of a ribbon web which is being driven from one reel to the other reel by the impact printer means for driving said ribbon. A keyed tenon projects from said housing and has an initial position and a second position; the keyed tenon is switchable from the initial position to the second position but irreversible from said second position.