Drag Pro's feature 3"dia 16 ga. steel tubing outer pipes. They are doublewall pipes using Road Burner's multi diameter stepped header design. Most inner pipes start at 1 3/4" dia. and then step to 1-7/8" dia. and finally to 2" diameter inner pipes. The stepped header design creates a "taper" which increases power thru more efficient exhaust "scavenging".