Regulating Valve: With height and diameter regulating valves, the extention tube can help you adjust the height of eyepiece from 67mm to 80mm and the eyepiece diameter from 41.5mm to 44.5mm. Accurate Machining: The extention tube and lens mount adapter are made of aluminum alloy and is easy to assemble and disassemble. It is durable and has long service life. Hollow Design: The use of the extension tube does not affect the focusing wheel, and the two sides of the extension tube do not affect the adjustment of the focusing hand wheel. M42 Male Thread: The camera extention tube comes with M42 male thread x 0.75mm, which is suitable for T2 lens adapter mount and T2 ring adapter DSLR. Wide Application: The extension tube and lens adapter ring are suitable for field observation and bird observation, and is helpful for visual photography.