Of all the components that make up this F-9 the O-ring,2.5x1.5 has the lowest price.
A sample from the products for the F-9 include: Piston,22 A, Caliper Sub Assy,, Screw, Bleeder, Spring,pad Rr.
Of all the components used in this assembly the Caliper Sub Assy, is the most expensive.