The LMT tactical adjustable rear sight offers a co-located sight picture to back up reflex sight systems. Forward and backward compatible with M16-type weapons families. Robust design and removable to fit any Mil-Std 1913 rail. Adjustments match current M4-type operation both in function and capability. NSN: 1005-01-548-5193 Contact your dealer or LMT directly at 309-732-9527 for estimated delivery time.