1The focusing helicoid adapter is the best choice for magnifying or altering lenses. It provides a focus system for lenses without a focus system. 2It can also be used as a macro tube to provide fine focus control for macro photography. 3The length of the focal length is 17mm/0.7in(min) to 31mm/1.2 in(Max), providing a 14mm/0.6in adjustable distance for lens focusing. 4Made of aluminum alloy, black anodized, long service life, very good hand feel. 5The inner wall of the focusing helicoid tube is matted to avoid the influence of reflected light on imaging. 6The M42 and M39 thread interfaces are universal and easy to transfer. 7The focusing helicoid tube can make the idle old lens can also be used for digital camera shooting. Condition: 100% Brand New Item Type: Focusing HelicoidAdapter Material: Aluminium Alloy Color: Black Weight: Approx. 82.0g Focusrange: 17-31 mm/0.7-1.2 in Interface: Female: M42 thread mount; Male: M39 thread mount 1 x Focusing Helicoid Adapter1. Please allow 13cm error due to manual measurement. Thanks for your understanding.2. Monitors are not calibrated same, item color displayed in photos may be showing slightly different from the real object. Please take the real one as standard.