Worst-case scenarios include bent U-bolts on the exposed threads bottom which will prevent you from removing the nuts. In this case, cutting off the U-bolts is the only answer. If new U-bolts are in order, many shops will use a cut-off wheel or a grinder to save time. In this case, a hacksaw is used to saw through the top of the U-bolt so that it's released from the housing. This is one of the reasons many products are made to protect the threads or change the direction of the U-bolts, which points the threads up out of harm's way.