Description: This tube useful for lens without focusing ring. And it can be use as extension tube. There is no electronic element in the adapter. and focusing must be manually control. The length of this helicoid tube is 17mm (min) to 31mm (max),it offers a total of 14mm movement distance for the lens focusing You can use M42 screw mount , such as or 42mm screw mount , and even . This Helicoid tube is useful for those without , Tube offers fine for photography. This focusing helicoid tube is made with 42mm front mount and standard 42mm rear mount and is made with light-weight alloy. Specification: Compatible With:M42 Lens & Camera Size:5.9 x 5.9 x 2.1cm Material:Aluminum Alloy Helicoid Tube Length:17-31mm Color:Black Package Includes: 1 Piece M42 to M42 Focusing Helicoid Adapter 17-31mm Note: Automatic diaphragm, auto-focusing will not operate correctly while using this adapter. Manual focusing with metering is with the adapter.