– tighten the nut with an adjustable collet wrench. This may be enough to loosen it;
- chop off the nut with a sharp chisel;
- if the nut is easily accessible, you can saw it along the axis; this method does not damage the bolt thread;
– carefully, without damaging the threads, use a special device for splitting nuts.
USEFUL TIP: Self-locking nuts with a Teflon insert are very often used in threaded connections. After unscrewing such a nut, replace it with a new one, since the locking function of the old nut is lost after unscrewing.