Bolt. NO.1. An Exhaust is a specialized Fastener designed to secure various components of an Exhaust System. including The Manifold. Catalytic Converter. and Exhaust Pipes. which is a specially designed shouldered. It is designed to Bottom against The Flange. which preserves The springs force (acting as a Locking Measure). compressing it. which (Can) Lead to failures during The High Temperature cycles found in Exhaust. These s always Mount Through the Flange.