A sample from the products for the Headlight include: Socket, Pilot Light, Grommet 839774310000, Nut, Adjust, Headlight Unit Assy.
The fifteen Xt350h (20kw) 1988 59y Germany 2859y-332g1 Headlight component parts are all listed in this schematic.
On this parts fiche the Screw, Rim Adjuster is the most specified component.