Mr. Gasket 7176MRG Copper Seal Triangle Collector and Header Muffler Gasket Prevents exhaust leakage between the header and collector flanges Bolt diameter is 2-1/2, bolt circle 3-1/2 and bolt hole 3/8 Triangle gasket with 3 bolt hole gasket Bolt circle size is 3-1/2" and bolt hole size is 3/8 Conforms to and seals minor surface irregularities