TEGIWA Donut Gaskets. Manufactured from PTFE impregnated stainless steel mesh these donut gaskets form a perfect seal between the exhaust manifold and cat/de-cat pipe and also for between the b-pipe/backbox. They are universal so can be utilised on pretty much any Honda system, and will eliminate any blows or leaks that may be occurring from the joint. We offer three sizes - 2", 2.25", and 2.5". The bore size is measured accross the internal diameter of the donut.