Standard 0.965 inch diameter fits 0.965 inch eyepiece and telescope. 0.965 inch 90 Degree Diagonal Adapter Erecting Mirror for Telescope. Designed for refractor and catadioptric telescopes, not for reflector telescopes. Features: - Color: Black - Size: 8.50 x 3.50 x 4.50 cm / 3.34 x 1.38 x 1.77 inches - Material: Plastic - Note: Screw is random style - Coated lens comes with cover; keeps your lenses clean for image fidelity - 90 degree diagonal mirror used with a refractor telescope produces upright images, though left and right are reversed; does not affect astronomical observation - More comfortable viewing orientation when observing from above; compatible with any 0.965 inch eyepiece - A 90° angled diagonal helps avoid neck strain when using the eyepiece Manufactured with professional technology to ensure product quality and long-term performance. Package list: 1 x Mirror