The lowest price component in this Taillight (kz750-b1/b2/b3) parts-list fiche is the Bolt 6x20.
A sample from the products for the Taillight (kz750-b1/b2/b3) include: Bolt, 6x22, Damper Rubber,l.b, Washer,6.5x20x1.6, Damper Rubber.
In this schematic the "Bolt 6x20" is used most often.