this is the iron sight, called a leaf sight, for the Colt or LMT M203 grenade launcher or flare launcher 37mm or 40mm barrels.
Mounts to a standard rail on M4 or similar rifle to aim the M203 projectile. Top Rail Mounted Leaf Sight for the M203, 50-250 meters. This is used item is superior condition. Not even sure it was used, but was covered in dirt and dust until we cleaned it up. The product has been in store for years. The manufacture date is most likely 10 or 20 years ago.