NcSTAR MSHRMDMOSR Mosberg 500/590 Receiver Micro Dot Rail Mount, Red Mossberg 500/590 micro dot base receiver Picatinny rail mount and ddab micro Red dot Reflex optic Combo Micro dot base on the receiver rail allow you to mount the ddab as low as possible on the rail Red dot micro dot Reflex optic with on/off switch Unlimited Eye relief