Made of Anodized Aluminum in Black finish with high quality. The length of this tube is 12mm(min) to 17mm(max),it offers a of 5mm movement distance for the lens focusing. This tube is useful for those lenses without focus ring offers focus control for macro photography. This focusing helicoid tube is made with standard M42 mount and is made with light-weight alloy. You can use M42 screw mount lenses, such as or 42mm screw mount lenses, and even enlarger lenses. It could be used as Macro Barrel. Instruction:Attach the Helicoid tube to the lens,then mount the combination of lens and Helicoid tube to the camera. This listing is for one piece Adjustable Focausing Helicoid M42 to M42 12mm-17mm lens adapter. Automatic diaphragm, auto-focusing will not operate correctly while using this adapterManual focusing with mode metering is ok with the adapter. Color: Black Material: Aluminum alloy Package Contents: 1* adapter Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.