Typical aftermarket exhaust manifold bolts are much shorter than stock which after numerous heat cycles can cause them to fatigue and start to stretch, leading to exhaust leaks and possible breakage after repeated re - torques. The finish and coating on most of these bolts can also lead to premature corrosion and zinc embrittlement. Replace damaged or corroded exhaust manifold bolts with BD's class 10.9 bolts and spacers which improve thermal durability to stand up to the heat and non - Zinc plated fasteners prevent zinc embrittlement.