Orion 07753 Deluxe Safety Film Solar Filter 4. Inch Inside Diameter (Silver) Explore the Sun safely through a telescope with this high-quality solar filter featuring Baader film in a sturdy aluminum cell Fits Orion Astro View 90, Apex 90mm, ED80T CF, Observer 70mm AZ and EQ, Short Tube 80, StarMax 90mm, Star Seeker III/IV 90 Make-Cass, and Meade ETX-90 telescopes Each filter is mounted in a foam-lined, clear-anodized aluminum cell featuring three equidistant securing thumbscrews for secure telescope attachment This filter has an inside diameter of 4.1 inch- it is designed to fit optical tubes with an outer diameter of 3.85 inches to 4.1 inches with included shim materials and securing thumbscrews 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