A nylon shim that sizes a FrameSaver clamp down to narrower tubing. Paediatric chairs and lighter frames often run smaller diameter tube, and without the right shim the clamp will rotate under load and the belt angle drifts.
The shim sits between the clamp and the tube, so it also takes the contact away from the frame finish. Nothing is drilled and nothing is glued, which keeps the chair the way the supplier delivered it.
Worth keeping a pack on the van, since tube size is the one thing that stops a hardware install in its tracks.
