This rail system offers three, 3-slot picatinny rails for Mossberg 590/590A1/Shockwave 12-gauge firearms. This kit includes a rail system machined from solid 6061-T6 billet aluminum and steel swivel screw. Both items are coated with color-matched Cerakote ceramic coating to match the firearm's factory finish and for increased durability. Attaches over the magazine cap for an easy 30-second installation. (Optics shown not included)