To help make the transition to a 3" focuser easier, and for use with their 3" 80mm Masuyama eyepiece, Kokusai Kohki of Japan has also developed a low cost 3 inch star diagonal mirror system that includes the 3" adapter sleeve for easy attachment to your (larger) SCT tube's (larger) visual back. Just screw the 3 inch sleeve on to your Celestron (11" or larger) or Meade (10" or larger) SCT telescope, slide in the star diagonal, then the Masuyama 80mm. and tighten all the lock screws, and you will have instant access to a whole new universe with your long focal length telescope.
As a convenience, also included is a 3 inch to 2 inch eyepiece adapter with this set. To avoid marring or scratching, the sleeves use a wrap around band to lock your eyepiece or accessory into position. Diagonal is made in China.