These are to replace the nylon sliders that the slide out bed rails "skate" across. There are usually 4 running across the front and the rear of the main body of the trailer. They are held in place with a single wood screw. The OEM's were a pan head screw and when the nylon wears out, you will have the screw grinding into your bed rails. They work well enough, though they are not a solid piece like the OEM's, but rather an inverted cup.
Attempted to use on a 2008 Fleetwood Avalon: the problem is that the wings slide back into the camper just a little more than this is wide. So I would have to build up the back to make it work. The other thing that I don't like is that it is held in place by a single screw so unless you glue it or something, it does want to rotate. As another noted it is not a solid piece but seems very strong despite that. Make sure to measure that gap between the box wall and the beds when they are pushed in before you order.
