The Rear Caliper (model K2/k3/k4) assembly is constructed from several parts from which the Caliper Assy,rr is the most expensive.
On this parts fiche the Bolt(8x18) is the most specified component.
The lowest price component in this Rear Caliper (model K2/k3/k4) parts-list fiche is the Screw(6x12).
