The JMI Telescopes Large Format SCT Visual Back Adapter for NGF-XTc allows 16" catadioptric telescopes with 4" male rear threads to accept the JMI Telescopes NGF-XTc focuser.
The front (where light enters) has 4" SCT style female thread, and the rear has a 4" threading matched to JMI's NGF-XTc focuser.
Made in the USA.