Orion 7715 1.25-Inch LRGB Astrophotography Filter Set A must-have telescope filter for safely observing the sun through a 10" Schmidt-Cassegrain without damaging your eyes Optical glass filter with 11.63" inside diameter fits snugly over your telescope's front aperture to block 99.9% of incoming sunlight so you can observer sunspots safely Glass elements are machine-polished and triple-coated with nickel-chromium stainless steel Each Orion telescope solar filter is mounted in a foam-lined aluminum cell featuring three equidistant securing thumbscrews, 4x 1/16" thick adhesive foam tabs, and 4x 1/8" thick adhesive foam tabs for customized friction fit to your telescope Note: All Orion solar filters are designed for use with an adequate friction fit attachment. Thumbscrews should ONLY be used to keep filter securely in place once a friction fit has been achieved