This is a GG&G, Inc. Shotgun Magazine Tube Components known as the Moss 590 Follower, model GGG-1439.
The GG&G Mossberg 590 Follower for 12 ga. shotguns is an enhanced follower manufactured with the Mossberg Tactical Shotgun Shooter in mind. Installs just like the factory 590 follower. No modification to the shotgun is required.
Features:
Better control of spring movement
stainless steel
Corrosion and wear resistant