Features: The extension tube set is used to obtain the correct image focal length or exact spacing required, therebysolving the spacing problem in astrophotography. By combining multiple extenders of different lengths, you get the right focal length to focuswith the camera or eyepiece. The M42x0.75 threadson both ends make it versatile. External thread M42x 0.75; internal thread M42x0.75; All metal construction and anodizing aluminium process;durable for long time use. The required spacing can be achieved by combining several T2-Extension Tube of different length;you can use 1 piece;2 pieces;3 pieces ;4 piece;5 piece;6 piece of the extension tubes as you like. Specifications: Type: Telescope T2 thread Extension Tube Male thread: M42x0.75mm Female thread: M42x0.75mm Length:approx 3mm 5mm 10mm 15mm 20mm 30mm Package Includes: 1 Set Telescope T2-Extension Tube Set note: Due to the problems of lighting effectsand shooting angles, there will be certain tolerances in the product, please understand. Please allow 0-1cm error due to the manual measurment.