i hate them. and i can't say that with enough vehemence over the internet to really convey how much.
it's a metal disk, with a hole offeset and a bolt through it. there are lips on the axle end of the control arm mounts (front = lower, rear = upper) that said disk fits between. when you turn the bolt, the disk will push against these mounts, and the axle will rotate accordingly due to the offset hole. pinch a quarter between your thumb and forefinger, off-center. spin it. they work like that.
yeah, i'd say between 3-4", you are definitely going to need to address your caster.