You will find people making them out of all sizes.
1.75 x .120 DOM or HREW is very popular.
Some like the 1.6 shedule 40 pipe style, very hard and rigid, tougher to dent than tube, but also heavier.
They look better the closer you can keep them to the body, yes there is the possibility of the cab bumping the exo in a roll, deal or add an inch of clearance.
The clearance may save your body, but it will also look worse, and create more drag on the road.
