The ST-28 Test Set was used for the troubleshooting and repair of NESTOR family equipment.  The KYK-38 keyfill device shown was used on the KY-28 and KY-38 equipment to load the encryption key into the mechanical memory system located behind the key loading door.  The KY-8 used a different plug-in module to load the encryption key.

 Photocopy courtesy of the C&E Museum, Kingston.