I made the assumption that the mask would fit on my Orion ED80T CF since it was 80mm and similar specs. Unfortunately it didn't fit inside our outside of the dew shield. Rather than scrap the mask, I just kicked out this quick collar and glued them together. Makes a nice sturdy mask that slides over the end of the telescope. I used a small piece of velcro (just the hoop side) to add a little cushion and make it fit snug.