The 6"x2" low impact caster wheel assembly with a black tire is unique to the Jazzy 600 ES. Unlike many mobility models, the 600 ES uses this same caster on both the front and on the rear articulating beam assembly.
I worry because it does not look like the ones that came with the chair. It is rubber in appearance and these I received are hard, not giving to the road I think. I just hope they work.