Features： [Broad Compatibility] Suitable for M52 mount lens and M42 mount adapter ring, providing a focusing system for camera. [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： Model: M52-M42(17-31) Color: Black Material: Aluminum alloy Product Size: 6.5 * 6.5 * 2cm/ 2.7 * 2.7 * 0.86inch Product Weight: 64g/ 2.2oz Package Size: 7.6 * 7.6 * 3cm/ 2.9 * 2.9 * 1.1inch Package Weight: 69g/ 2.4oz Note: Only the camera lens adapter ring is included. Package List： 1 * Adapter Ring