Features: Made from quality aluminum material with anodizing on surface The length is 17mm(min) to 31mm(max), with 14mm movement distance for the lens focusing Used for those lenses without focus ring, ing fine focus control for macro photography Made with standard M42 mount You can use M42 screw mount lenses, such as Carl Zeiss or Pentax 42mm screw mount lenses, and even enlarger lenses Can be used as Macro Barrel Easy to install: attach the Helicoid tube to lens, then mount the combination of lens and Helicoid tube to camera Note: Automatic diaphragm and auto-focusing will not operate correctly while using this adapter. Manual focusing with A/M mode metering is ok with the adapter. Specification: Color: Black Material: Anodized Aluminum Length: 17mm-31mm(14mm movement distance for focusing) Focus: Manually Package Includes: 1 x M42 to M42 Focusing Helicoid Ring Adapter Packing list 1 x M42 to M42 Focusing Helicoid Ring Adapter