The GM replacement steel tubs have nuts welded to the tubs for securing them to the fender lip. Obviously you can’t weld to carbon fiber, so the Anvil tubs have nuts bonded to the edge. The stock steel GM tubs weighed in at 10.2 lbs. each, and our hybrid carbon/fiberglass Anvil tubs came in at a hair over 5 lbs. each. Add it all up, and that’s 10 lbs. off the nose of our ’68. The total carbon tubs are a bit lighter, and the full fiberglass versions a bit heavier.