The Flex System from Mossberg uses coordinated accessories with the innovative Tool-less Locking Sytem (TLS). This system of modular guns and accessories will change the way you use your Mossberg all together. The TLS is a series of three connectors that allow shooters a simple and quick method of switching stocks, forends and recoil pads on the fly.This is the Railed Tactical Flex Forend for the Mossberg Model 500 and 590 FLEX shotguns.