the nut could have had a bad spot in the thread that tore up the axle threads. normally if things are stressing threads in a nut then it's all the threads the nut is contacting and not just part of them. always make sure the threads are clean on the nut and the bolt (axle in this case) before making the connection. any machinist can tell you that it doesn't take much contaminants to lock parts together forcing you to destroy them to get them apart.