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 medium sized Flex Standard Hunting Stock for the Flex series Mossberg Model 500 and 590 shotguns.