TD-339 (Surveyor Vernier) Rocket Engine

The Thiokol Rocket Motors Division TD-339 vernier engine was used by the Surveyor series of spacecraft to provide a midcourse correction burn, to position the spacecraft's main retromotor to the proper attitude to slow the spacecraft for a soft lunar landing, and to provide the Surveyor spacecraft's final thrust during its terminal descent.

Mark's TD-339 is mounted to the lid of its transport case, exactly as it would have been received by JPL from the manufacturer.