I haven't measured, but having both a 1500 and a 3500, that front sway bar hasn't caught my eye. I figured they were the same. Maybe I'll take a peek tomorrow when I have them in the same place at the same time if I remember.
It's not a huge difference, I think 1/2 ton is 1 1/16" an 1 ton is 1 1/4" but I think depending on the gvwr they could have gotten different ones too as every one an a while I see 1 1/8 listed out there too.