Trinity Polymer Shell Holder With Base Mount For Mossberg 590 12 Gauge Pump.Great for slug shooting, hunting, home defense, security, or tactical shotgun use Fits standard Mossberg 500 and 590 Models 12 gauge with included hardware. Installs via included set screws into the Mossberg factory mounting holes No modifications are required to the weapon for installation. A tough waterproof shell carrier is mounted to an aluminum mounting plate that installs directly on the shotgun receiver. The shell holder is made of corrosion