2007-11. 4.0 LITER. Left.6 CYLINDER. Muffler & pipe stud. Right.6 CYLINDER. 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. AND pipe. and Spring.