Ken - that is almost how the end of the thread on the knee elevation screw looks on my mill. The top part of the thread in the nut is chopped out and I can only think that the knee was raised so the screw disengaged from the nut and then all hell has broken loose on the way down. I should take a picture of it. Last thing I want to do is wreck a new nut.
Hunting American dentists since 2015.