Parts such as the Rear Wheel: Sprocket,rr, Bolt(6x33), Shoe,brake, Bearing are included in the Gp100 1978 (c) (e01 E02 E06 E13 E14 E24 E30) Rear Wheel parts fiche.
In this schematic the "Bolt(8x33.5)" is used most often.
The Rear Wheel is made up of components including this Hub, Wheel which is the most expensive.