Hi Allan,
That,s exactly what Sparey said about the fit of the nut,that one or other of the threads could be tight,but there was no way of knowing which one,so the only way was to take another pass from one and try it. If that did not work,take a pass from the second thread and try again.
You,ve really got me interested in this stuff now,time to leave the grass for another day. Cheers !