Aluminum header collector gaskets designed with a 2.5" inside diameter. Gaskets are ideal for race, street or tow vehicles. The material creates a tight seal that's leak proof! <conforms easily=" irregularities=" span=" surface=" to="> These collector flange gaskets are reusable! Made from dead soft aluminum-won't shrink, deteriorate, blowout or burnout. Each kit comes with 2 gaskets and six 3/8 nuts and bolts.