Check out any of the seventeen Lower Crankcase components enlisted.
Parts such as the Lower Crankcase: Screw,pan,6x16, Bolt,drain.cock, Washer, 14m/m, Crankcase (lower) are included in the Cb350p4 Police Type General Export / Kph Mph Lower Crankcase parts fiche.
The Washer,plain, 6mm is the lowest priced item on this Lower Crankcase schematic.