Both Driver Side Part A and Passenger Side Part B Gaskets; GM GMC truck/SUV/Hummer LS '99-'12 , Header/Manifold to-Exhaust Pipe Flange, 2 Piece Set 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 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