The rubber nut may be for the anntenna wire to exit the fuse and flex a bit. I used the standard pushrods that came with my 4*40 with no problems at all. I did insert a piece of wire into the inside of the hollow tubes at the rear end to eliminate any flexing. I get a nice full ele and rudder movement, so much in fact that the plane will snap like crazy with full ele movement at times.

Ernie