Parts such as the Seat: Nut, Seat-assy,black/white are included in the Kdx50-a2 Kdx50 2004 Usa Canada Seat parts fiche.
In this schematic the "Nut" is used most often.
The most reasonably priced component used on the Kdx50-a2 Kdx50 2004 Usa Canada Seat is the Nut.