This is an excellent 1.25-inch double-threaded focuser with a 10mm adjustment stroke. It is light and compact, made of all metal, and durable. During the focusing process, the inserted CDD eyepiece or zenith mirror remains non-rotating and only makes linear movements, which is conducive to observation and astronomical photography. The meticulous craftsmanship makes its micro-focusing extremely precise, and it remains smooth and stable even at huge magnifications. 1. double-helix focuser 2. High-precision double-helix focuser for guide mirror/finder interface 3. Solution to slow focusing of telescopes or telephoto lenses 4. Made of all metal, durable Inner diameter 1.25inch Stroke 10mm Adjustment accuracy 0.05mm Top external thread M42x0.75 Bottom interface 1.25 inches (31.7mm) Bottom inner ring external thread M31x0.5 Minimum height 46mm Maximum height 56mm Colour:Black Material:Metal Package Contents: 1 x Telescope Double Helical Focuser