The thermal ribbon cassette is attachable to a thermal printing apparatus, the cassette housing is formed by a forward section attached to a rear wall to define a chamber. A supply spool is rotatively mounted to the forward section and the rear wall in the chamber. The supply spool has an ink transfer ribbon continuously wrapped there around and a number of interrupters continuously formed around the edge of the spool. A drag spring is mounted to the rear wall and biased against the interrupters for providing a rotational drag force. The take-up spool is rotatively mounted to the forward section and the rear wall in the chamber, the ink transfer ribbon has one end fixably mounted to the take-up spool and a portion extending through slots in the housing such that a portion of the ink transfer ribbon extends externally to said chamber. A locking gear arrangement is provided for preventing rotation of the take-up spool except in a forward direction.