The original plate or block bearing the design engraved in correct dimension is the original or master die. It is used sparingly, to provide duplicates sufficient to become (after additions to the engraving) master dies for each of the several denominations in a series. These may be transferred by means of roller dies to a steel plate, or to provide working dies to make moulds for electrotyping.

The terms Die I, Die II, etc., are used to distinguish actual stamps deriving from dies, or replicas of dies, which have been subjected to small alterations.