01-22-2014, 06:38 PM
Probably just excessive wear combined with a low rate of thread percentage for engagement. Looks like it was poorly lubricated.
The end of the thread appears to have been torn off. I don't know if the weight of the knee is hanging on it (doubtful) but perhaps when someone tried lifting the knee off the screw before it was fully disengaged from the nut that would have done it. You could just grind it clean to give it a good start without mashing a new nut. Truthfully I'd be looking for a new screw as those thread look beat to crap.
The end of the thread appears to have been torn off. I don't know if the weight of the knee is hanging on it (doubtful) but perhaps when someone tried lifting the knee off the screw before it was fully disengaged from the nut that would have done it. You could just grind it clean to give it a good start without mashing a new nut. Truthfully I'd be looking for a new screw as those thread look beat to crap.