Standard 1.25 inch diameter fits for 1.25 inch refractor telescope and 1.25 inch accessories(eyepiece,barlow lens etc.) The diagonal mirror provides a comfortable 90-degree viewing orientation when observing the night sky through a refractor telescope Semi-metallic body ensures high cost performance and stable and reliable quality High quality coating and pure optical Mirror maximize the light transmission.Dust covers are included to protect lenses from dirt and scratches Please note:The diagonal only for refractor telescope.Not recommended for using in reflectortelescopes!!!