NORTH AMERICA BUILT. W/O PRIME PLUG-IN. 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. Exhaust Muffler Bolt. Part cannot be reused/reinstalled. FLANGE. AND. Mount.