On this parts fiche the Screw is the most specified component.
Some items from this specific schematic: Bolt(10x39), Case,chain, Nut, Spacer,rr Swgarm Pivot Ctr.
The most reasonably priced component used on the Gsf1200s Bandit 2004 (k4) Usa (e03) Rear Swinging Arm is the Washer(12.5x20x1).