From what I can tell, they are both the same (maybe slightly different diameter, I forget the measurements), a metal tube welded to the frame, a rubber bushing that seemed to be bonded to it, with a metal sleeve for the bolts to the bracket.
If you do want another one, I found an easy way to get them out is to use a drill with a small bit (1/4", long enough to go through). Aim it right at the outside edge of the bushing, right up against the metal tube, drill slowly to get the drill all the way through, then keep the drill going slowly and let the rubber grab the drill bit, and it'll work it's way around the bushing right next to the metal tube. That free's the bushing, pull the drill out, and hammer the bushing out (doesn't need much effort as it's free of the tube.
2004 GMC Sierra 3500 C&C, added 4WD, 6.0L gas, Extended Cab, SLE, Transgo 4L80e-HD2 kit installed
Whee! Dually Club Member #1109