This is a one piece mount for Aimpoint Micro sights that provides a lower 1/3 co-witness on AR15 style rifles. It has been replaced by a newer model.
The Daniel Defense Aimpoint Micro Mount is designed to work in conjunction with Aimpoint's popular Micro optics, this mount is designed to attach to your flat top upper receiver. Its lightweight, essentials only design offers a snag-free, low-profile, reversible mounting option for shooters that do not require or desire a quick attach/detach mount. The mount features a recoil lug that minimizes sheer forces on the factory mounting screws. Machined from 6061 aircraft grade aluminum and Military Specification Hard Coat Anodized, it's both lightweight and durable.