Mr. Gasket Copper Seal collector gaskets are made from Dead-Soft Copper. Collector and Header Muffler Gasket - 2 1/2" diameter - Copper Seal Collector/header muffler gaskets are designed to prevent leaks between header and collector flanges. Designed for high-performance street, drag race, oval track and turbo-charged (extreme heat) applications. Bulk gaskets are sold individually, 1 pc.