1-1/2 Round Port; Chevy V8 4.8L, 5.3L, 5.7L- LS1, LS6/6.0L- LS1, LS2 Vortec, 1-1/2 RP, For Weld Bead Headers, 2/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 For use with raised weld bead headers; additional sealing material is provided around the weld bead to provide a better seal 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