This is a Yankee Hill Machine Co Sight known as the Same Plane Flip Front Sight, model YHM-9627.
AR-15 Same Plane Flip Front Sight- This durable" all steel sight mounts on the same plane as the rear sight to give you a backup iron sight. The sight folds out of the sight line with the push of a button and flips and locks in the deployed position with ease. Mounts quickly and easily with the included thumb screw. Accepts all standard AR sight posts and hardware (included).
Features:
Same plane flip front sight
Picatinny mount
