One challenge to welding on factory frames is that many times they’re painted inside and out. You can clean the paint off of the outside, but there’s still paint on the inside that can get pulled into a weld. When paint gets pulled (by heat) into a weld it creates porosity in the weld. No good! To avoid that problem, rings were made that allowed the tube to be welded to the radiator crossmember without getting paint pulled into the weld. This tube pierces through the radiator crossmember and will eventually tie into the main bumper structure.
