There should be a set of those parts in each fork slider. They are the damper tube, bottoming-out spring and 'lower stop', a silly name for a part which centres and secures the damper tube. A screw holds the tube and stop in place.
FWIW,
That's a Top Out spring to dampen "topping-out" and that lower stop is not for centering and securing the damper, it provides a Hydraulic "stop" (aka "oil lock") by blocking the oil path when the tube starts to cover the taper of the lower stop