In the beginning two inch. Later I went with a Dobinson three inch which is actually closer to four. The bushings worked very well until I went part time. I now needed a bit more caster to make up for the lack of front pull. 70mph down Cajon Pass was white knuckle at times.
Mine were from Slee and I went about four years before I bought my new arms. Looking at them they were not bad. I still could have gone a year more before I would have replaced them.