The Meopta MeoStar 2x Mag Doubler screws into the threads that are upon your MeoStar binocular's eyecup to double the effective magnification. An 8x binocular becomes a 16x power unit, a 10x turns into a whopping 20x and so forth. It works with all Meopta 32mm, 42mm, 50mm and 56mm MeoStar series and is a handy accessory to keep around.