1-1/2 inch width x 1-1/2 inch height Raised D Port; Chevy V8 GM Performance Circle Track Motors CT355 603 /CT400 604 Raised D Port| 2/Set Circle track applications 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 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