RCD fuel pump extensions use a pressed-in alum. thrust bushing to set cam thrust against and in the event that the racer acquires a pump extension that has had the bushing machined or has been lost, not to fear RBS carries this part to put you back on the track.
Bushing is made from billet alum., measures 1.455" O.D., .300" deep where it presses into the fuel pump extension, 1.700" O.D. x .110" thick where the bearing and washers ride against with a 1.130" I.D. hole.