The NcStar Mossberg Shotgun Receiver Rail is designed to fit Mossberg 500/590 models with the factory pre-drilled holes on top of the shotgun receiver. Mossberg 500/590 Receiver Picatinny Rail Mount for mounting Optics to your Shotgun Low Profile Picatinny Rail design with See-Through Channel allows you to still use the Front Bead Sight Screws included for mounting rail to Shotgun Receiver All Aluminum Construction. Black Anodized finish Length: 5.4" Weight: 1.3 oz.