The Nut,flange,6mm is the cheapest item from this partsfiche.
In this schematic the "Rubber Set Stop" is used most often.
Parts such as the Seat: Stay A,rear Seat, Seat Assy,main, Bolt,hex,cap 6x16, Nut,flange,6mm are included in the Vt1100c2 Shadow 1999 (x) European Direct Sales / Kph Seat parts fiche.