The NCStar AR-15 Detachable Rear Sight is a solid and dependable back-up fixed A2 rear sight, the NCStar MARDRS does not take up much of your valuable Picatinny rail space. You can have a back-up iron sight ready to go at a moment's notice and have space for a red-dot/reflex/holographic optic on your AR-15 upper receiver. The MARDRS will fit virtually all AR-15, M4, and M16 flattop Picatinny rail upper receivers. A2 rear sight assembly with large and small rear aperture. The A2 rear sight is fully adjustable for elevation and windage with knurled click adjustable controls. Large steel thumb nut and steel rail clamp for positive and secure attachment to your upper receiver. Precision made A2 rear sight. The mount and rear sight is made from high quality aluminum and steel.