I grabbed the door handle to open it - and it came off in my hand ... The lathe had been recently improved. Batches of bolts could now be cut on different lathes, and they would all fit the ...

The bolt is an M42 size with a 40 mm pitch, with grooves cut in both directions to allow left-handed and right-handed nuts to be threaded. The large pitch means that instead of a single continuous ...

But instead of cutting new threads ... then back it off a full turn. This will dislodge the debris from the teeth. Don’t try to rethread the entire bolt, hole or nut in one operation.