3.5 LITER. A spring Bolt, which is a specially designed shouldered Bolt with matching spring and nut. It is designed to bottom out against the flange, which preserves the spring's force (acting as a locking measure) without over-compressing it, which can lead to failures during the high temperature cycles found in exhaust. These Bolts always mount through the flange, with a nut on the backside. An exhaust Bolt is a specialized fastener designed to secure various components of an exhaust system, including the manifold, catalytic converter, and exhaust Pipes. Center muffler. Exhaust and Spring. Flange. Muffler. Tail.