This Astro-Physics visual back threads onto your 8", 9.25" or other SCT with the standard SCT rear cell. It allows you to use 2" accessories that slip in, i.e. 2" diagonals, Barlows, 2" eyepieces or CCD camera. The brass locking ring and 2 thumbscrews set this adapter apart from others on the market. It will hold your expensive accessories with ease. Also fits DayStar T-Scanner cover that has male T-thread. This adapter measures 2.06" in length.