It wasn't the lenght of the bolt but the lenght of the threads. A couple of the next to shortest size had threads that did not extend as far up the bolts length. The bolt would stop before tightening down. The washers would still spinfreely after the bolt could not be further inserted. The car feels great. Its raining lightly out so theres no traction, but it sure makes for some fun driving. Can;t wait till it's dry out. Everyone I've shown says they look great. They make the engine look like it makes some real power. As it does!