[Focus Length] Can be adjusted from 17mm to 31mm, support manual focusing, satisfying your various needs, flexible and convenient to use.[Macro Extension Tube] Can be used as an old lens and macro extension tube, perfect for macro photography, digital camera photography, and more, easy to install and use.[Premium Aluminum Alloy Construction] Made from high-quality aluminum alloy with advanced anodic oxidation technique, sturdy and durable.[Compact Size and Light Weight] Max. 7cm diameter and weights only 99g, convenient for storage and carrying.Specifications xff1a;Brand: AndoerModel: M52-M42(17-31)Color: BlackMaterial: Aluminum alloyProduct Size: 6.5 * 6.5 * 2cm/ 2.7 * 2.7 * 0.86inchProduct Weight: 64g/ 2.2ozPackage Size: 7.6 * 7.6 * 3cm/ 2.9 * 2.9 * 1.1inchPackage Weight: 69g/ 2.4ozNote:Only the camera lens adapter ring is included.Package List xff1a;1 * Adapter Ring