The Bolt, Flange(3jk) is the lowest priced item on this Side Cover schematic.
With two applications this Screw, With Washer(3yj) is the most specified part.
Parts such as the Side Cover: Panel 1, Cover, Side 2, Bolt, Flange(3jk), Panel 1 are included in the Yz400f 1999 (x) Usa Side Cover parts fiche.