null Features: Suitable for M42 lens without focusing ring. Can be used as a macro extension tube. No electronic elements, manually check the opening and focus. Aluminum alloy material, CNC precision machining, durable and sturdy. Easy to install and simple to use. Technical specifications: Material: Aluminum Alloy Lens compatibility: M42 screw mount lens Length: 17mm-31mm / 25mm-55mm / 36mm-90mm (optional) Packing list: 1 * Adapter Ring