The component with the lowest price in the SEAT ('78 D1) schematic is the Washer-spring,6mm.
On this parts fiche the Bolt Upset,6x16 is the most specified component.
Parts such as the Seat ('78 D1): Washer-plain,5mm, Bolt,6mm, Damper Rubber, Lock Assy,seat are included in the Kz1000d1 Z1r 1978 Canada Seat ('78 D1) parts fiche.