TacStar Shotgun Rail Mount with SideSaddle, 12 Gauge, Fits Mossberg 500/590, Black Finish 1081029 Ultra-rigid" this innovative lightweight aluminum unit straddles both sides of the receiver and is crafted with a non-glare anodized finish. The top Picatinny rail can mount a variety of accessories" yet is designed to sit just high enough to allow continued use of the shotgun's bead sight.