The pi disc — a flat ring with a central hole — is one of the oldest recurring forms in Chinese jade, found in burials that predate written records. Nobody is certain what the earliest ones meant; the name most often attached to the modern version means peace.
Because it is a simple ring, it is also one of the cheaper forms to make, and the quality difference between pieces is mostly in the polish and the evenness of the hole. Nephrite throughout. Small and light at 60 g, so it is unlikely to obstruct a view.