Magpul Industries MBUS Back-Up Rear Sight Gen 2, Fits Picatinny Rails, Flip Up, Olive Drab Green MAG248-ODG
Specifications:

Type	Rear
Frame Material	Polymer
Frame Color	OD Green
Firearm Fit
Base Configuration	Picatinny Rail
Style	Folding
Front Material
Rear Material
Front Color
Rear Color
Rail Size
Windage Adjustment	Yes
Elevation Adjustment
Fiber Diameter
Firearm Type	AR15/M16