The Seat Tail Box (gsx-r750k5) is made up of components including this Box Assy,seat Tail(blue) which is the most expensive.
This part-list fiche shows all the components that make up the Gsxr750x 2005 (k5) Usa (e03) Seat Tail Box (gsx-r750k5) .
In this schematic the "Cushion" is used most often.