If you have thread-on accessories for an SCT and own one of the Astro-Physics refractors, a Ritchey-Chretien with an Astro-Physics focuser or built your scope with the Astro-Physics 2.7" focuser, you will appreciate this item. This adapter threads into the Astro-Physics drawtube and has SCT threads on the accessory side.
The ADA204 is also popular with owners of Finger Lakes Instrumentation CCD cameras. It can be used with several configurations of Astro-Physics CCD Adapters and 2.7" Extensions to reach proper back focus distances for the particular combination of components you are using.
This adapter has a net spacing distance of 0.3" (7.6 mm).