As vengeful noted, Shrockworks makes them with round tubing -- we have a set on the Xterra... Hubby likes the round as it's easier to use for a highlift point, no matter what angle your truck is stuck on...
Sliders sticking out: I know he has also used his to round a corner where there is a big rock on the inside, and because of the sliders was able to use them, instead of worrying about the side of his truck.
We need sliders for my pathy, before I go playing smashup derby with my rockers... as nice as it would be to have round tubing, I'll likley go with square, simply because it's easier. (no pipe bender for that size)