Fotasy 17-31mm M52 to M42 Lens Macro Helicoid Adapter, 52mm Focusing Helicoid Extention Tube, 17mm to 31mm, 14mm Max Movement, fits M52 52mm Screw Mount Lens
M52 52mm to M42 42mm Adjustable Focusing Helicoid 17mm - 31mm.
The length of this Helicoid tube 17mm (min) to 31mm (max), it offers a total of 14mm movement distance for lens focusing.