Feature 1 The focusing helicoid adapter is the best choice for magnifying or altering lenses. It provides a focus system for lenses without a focus system. 2 It can also be used as a macro tube to provide fine focus control for macro photography. 3 The 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. 4 Made of aluminum alloy, black anodized, long service life, very good hand feel. 5 The inner wall of the focusing helicoid tube is matted to avoid the influence of reflected light on imaging. 6 The M42 and M39 thread interfaces are universal and easy to transfer. 7 The focusing helicoid tube can make the idle old lens can also be used for digital camera shooting.Condition: 100% Brand NewItem Type: Focusing Helicoid AdapterMaterial: Aluminium AlloyColor: Black Weight: Approx. 82.0gFocus range: 17-31 mm/0.7-1.2 inInterface: Female: M42 thread mount; Male: M39 thread mount Package List1 x Focusing Helicoid AdapterNote1. 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.