US Patent 8202255 Dose display mechanism for a drug delivery device

A dose display mechanism for a drug delivery device is disclosed. The display mechanism has an elongated dose setting dial with both an external helical thread and external linear grooves extending from one end to the other end. A counter ring is mounted surrounding the setting dial. The counter ring has ribs on its inner surface which engage the grooves and permit the counter ring to move axially along the setting dial but prevent it from rotating relative to the setting dial. Indicia, in the form of digits, are arranged helically on the outer surface of the dose setting dial. The digits are spaced at a pitch which corresponds to the pitch of the external helical threads.