On this parts fiche the Screw-pan Head,6x18 is the most specified component.
This schematic depicts all components used in the Zx600c10 Gpx600r 1997 Fg Oil Pump partslist.
The most reasonably priced component used on the Zx600c10 Gpx600r 1997 Fg Oil Pump is the Circlip-type-c,11mm.