Parts such as the Rear Master Cylinder: Screw, Diaphragm, Pin, Hose,reservoir Tank are included in the Gsx600f Katana 2004 (k4) Usa (e03) Rear Master Cylinder parts fiche.
The Rear Master Cylinder assembly is constructed from several parts from which the Cylinder Assy,rr Master is the most expensive.
In this schematic the "Washer(10x15x1.5)" is used most often.