Guntec USA has been manufacturing AR-15, AR-308 and AR 9mm accessories since 1989. Their goal is to distribute excellent quality, at an economical value. Features1913 Picatinny Rail Flat TopWill Match Up With Any Brand 9mm Lower Receiver Such As New Frontier, Palmetto State Armory, & Circle Quarter 10Ejection Port Opening Measurement : 0.61" Width X 2.30" LengthSmooth "Slab Side" Design