Astro-Physics 2-inch Standard Visual Back
This visual back fits rear cells that have a 2-inch opening with a 24 TPI (threads per inch) male thread and is 2.06-inches long. It can be used with the 8-inch, 9.25-inch (except the 9.25-inch Celestron EdgeHD), or other SCT with the standard SCT rear cell. It can also be used with the Maksutov-Cassegrain scopes from Telescope Engineering Company (TEC) that have this specification.
This AP visual back allows you to use 2-inch accessories that slip-in, i.e. 2-inch diagonals, Barlows, 2-inch eyepieces, or CCD cameras. The ADASCT also fits DayStar T-Scanner cover that has male T-thread.