Parts such as the E-21: Lever, L. Throttle, Carburetor Assy,l, Washer 7m/m, Screw,cross 5x10 are included in the Cb450k3 Japan E-21 parts fiche.
With four applications this Washer,spg.,5mm is the most specified part.
The most reasonably priced component used on the Cb450k3 Japan E-21 is the Washer 7m/m.