The most reasonably priced component used on the Cb500k2 Four 1973 Usa Rear Wheel / Driven Sprocket is the Nut.hex 10mm.
On this parts fiche the Spoke A, Rear is the most specified component.
A sample from the products for the Rear Wheel / Driven Sprocket include: Spoke B, Rear, Nut.hex 10mm, Flap,x-18a, Tube3251350-18tr6.