Description: This focusing helicoid tube with M52 front mount and standard M42 rear mount, can be adjusted from 17mm to 31mm, support manual focusing, satisfying your various needs, and convenient to use. Useful for those lenses without focus rings, offers fine focus control for macro photography. It can be use as macro extension tube, By moving the l.ens further away from the film or digital camera sensor, the l.ens is forced to focus much closer than normal, perfect for macro photography, digital camera photography. Use this tube with your normal l.ens and you will get the quality, which is as good as the original l.ens and the size, sharpness and versatility is perfect for the macro and close-up pictures. Made from high-quality aluminum alloy with advanced anodic oxidation technique, sturdy and durable Specification: Type: M52 to M42 Mount Focusing Helicoid Rings Adapter 17-31mm Extension Tubes Front mount: M52 screw mount female Rear mount: M42 screw mount male Length: 17mm to 31mm (14mm movement distance for focusing) Focus: Manually Material: Aluminum alloy Size: 6.5 x 6.5 x 2cm/2.6 x 2.6 x 0.8 inch Package Includes: 1 Piece Focusing Helicoid Rings Adapter Note: 1.Please allow 1~3 cm error due to manual measurement, thanks. 2.Due to the difference between different monitors, the picture may not reflect the actual color of the item. Please understand, thank you.