Parts such as the Seat (model N : F.no. 107282~): Pin, Bolt 5x16, Washer, Lock Washer are included in the Gt250e 1981 (x) (e01 E02 E04 E05 E16 E17 E18 E21 22 24 25 30 39) Seat (model N : F.no. 107282~) parts fiche.
On this parts fiche the Nut is the most specified component.