Remflex 8003 Universal Exhaust Gasket, (Set of 2) 3-1/2" Pipe; Universal 3-1/2 Collector Flange, 3 Bolt Holes, 3-25/32" Bolt Hole Spacing, 2/Set Heating and cooling of the exhaust system causes header and manifold flanges to warp resulting in gaps between the head and header which Remflex exhaust gaskets seal completely due to the thickness and compressibility of the 100 percent flexible graphite Remflex exhaust gaskets come in a standard 1/8 inch thickness and are designed to crush 50 percent allowing them to fill any pits or gaps in the flange surface up to 1/16 inch The aluminum cylinder head and steel header or manifold combination are configurations that readily cause gap issues in the mating flanges due to contraction and expansion of the dissimilar materials; Remflex exhaust gaskets fill those gaps permanently There are no rubber binders or composite materials in Remflex exhaust gaskets so they will not shrink or harden due to time or temperature eliminating the need to go back and continually retighten your flange bolts