I've never seen that before? I don't really know how it would be used. I don't believe that it should be used to help your Chi Sau. Your force should be directed forwards not outwards as my initial response (just seeing the ring) I imagine just holding the ring up in position while rotating your hands. Your movement may look proper on surface but the direction of force would be totally wrong. I hope that IÂ’m jumping to the wrong conclusion on its purpose... and it is used for something completely different than practicing Chi Sau.
Maybe someone with more information on this tool can shed some light on how it is used.