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. Complete with dual aiming apertures ideal for moving target engagements and limited visibility or normal firing situations. 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.