Orion 7783 12.31-Inch ID Full Aperture Solar Filter A must-have filter for safely observing the Sun through an 11" Schmidt-Cassegrain telescope without damaging your eyes Solar filter with a 12.31" inside diameter fits snugly over your telescope's front aperture to block 99.999% of incoming sunlight 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