Features: 1.25 inch calibration eyepiece is of short size, made from aluminum alloy and finished by CNC manufacturing. Used to calibrate the optical axis of a refractor, put the collimation eyepiecre into the tube. Make sure the black spot is in the center of 2 lines of collimation eyepiece. Please adjust the screws if it is not in the center, in this way, you will collimate sucessfully. A wonderful accessory for both photography and astronomy lovers. Specifications: Condition: Material: Aluminium Alloy Color: Black Caliber Diameter: 1.25in * Suitable for refracting telescope length: Approx. 64 mm / 2.52 in Diameter: Approx. 35 mm / 1.38 in Weight: Approx. 92 g Package List: 1 * Eyepiece