[Centered Fixation]Three metal posts secure the mask firmly in place, ensuring perfect alignment for precise focusing. [Highly Versatile]Compatible with telescopes with outer diameters of 84-115mm, this focusing mask suits reflectors, refractors, and SCTs for a range of observing needs. [3 Screw/Fastener Quick Mount]Easily install this mask using the three bolts, and enjoy straightforward removal after your observation sessions. [Lightweight Design]Constructed from a 1mm aluminum alloy, it weighs only 57g, maintaining your telescope's balance without excess weight. [Star Guided Focusing]Light diffraction creates patterns for precise focus adjustments, enhancing efficiency even under poor visual conditions.