Parts such as the Front Fork (gs400c,ec,n:~f.no.71031) (gs400en:~f.no.504509): Cylinder,front Fork, Nut, Damper Assembly,right, Ring,piston are included in the Gs400e 1978 (c) (e01 E02 E04 E17 E18 E21 E22 E24 E25 E30 E34 E39 Front Fork (gs400c,ec,n:~f.no.71031) (gs400en:~f.no.504509) parts fiche.
On this parts fiche the Stud 8x25 is the most specified component.