I bought this to use with the 20x80 Celestron binoculars. They fit great over the actual eye cup. You can remove the eye cups to install them from the back or carefully put them over by carefully stretching them a bit at a time as you go around the oversized eye cup.
I've been buying these for years, putting them on all my binoculars. They're nice during the day, and VITAL at night for cutting out distracting light.