New generation super slim flip-up rear sight for the AR-556® and other firearms equipped with Picatinny rails. Spring loaded posi-Lock Design with side plunger release for positive flipping/folding makes it fast and easy to compress the plunger to unlock and fold down the sight when not in use. Robust posi-lock plunger coupled with spring-activated ball bearing guarantees zero retention. Low profile 3mm locking bolt and mounting deck attaches securely to any Picatinny rail. Precision-machined from aircraft grade aluminum with black anodized finish. Designed to match the AR-556® Low Profile Flip-Up Front Sight (18140) on same level plane applications, either directly on the handguard or on a high profile Picatinny rail gas block. Made by UTG Leapers.