I'm guessing none. There is a rubber bushing built into one of the arms but no other bushings. There may be a curved plastic part inside one or both ends of the pivot tube - one for ball stud and one for the special bolt on the frame end
I know this is an older thread, but there are two nylon "seats" that go on the inside of the z bar. Both go on the frame side, one on each side of the ball stud to create a knuckle. Russ