These rear frame supports replace the original frame supports, which were made of 1/8” steel and had slotted holes for frame tolerances. Although the idea was a good one, the design of the stock frame support was non-effective. These tubular adjusting sleeves are made of 1” O.D. .125 wall tubing and jig fitted for proper fitment. These supports are not just for drag cars, but for any car, to give you the stability and rigidity the rear end needs.