I have a flatbed to install on my 2002 7.3 The bed is rusted almost ready to blow off. So I bought a Duramag 7' Aluminum flatbed. I ordered these sill tubes from the manufacturer of the flatbed that can be welded to the 2 long frame rails under the flatbed. I got them from the company and they weld them on for flatbeds ready to go on ford shortbeds. They go in front and behind the wheel hump on both sides and are to be welded to the flatbed frame rails. So they sent me the tubes and one set is 1/4 higher that looks like it goes up front. one side has 2 pieces to allow for the fuel fill line. These are the 1/4 inch higher tubes. 2 tubes for the rear are 1/4 less thickness. I have pretty much figured where they go but was wondering why the difference in the thickness. Maybe the frames naturally goes downhill on the truck and this levels it out? thanks for any help Jeff