If sides of a nut are damaged, use special tools:

– clamp a nut an adjustable collet key. Perhaps, it will be enough that to turn off it;

– cut down a nut sharply perfected chisel;

– if the nut is well available, then it is possible to saw it along an axis, at such way the bolt carving is not damaged;

– carefully, without damaging a carving, use the special device for splitting of nuts.

Good advice In threaded connections very often apply самоконтрящиеся nuts with a teflon insert. After an otvorachivaniye of such nut replace it new as functions of a zakontrivaniye of an old nut after an otvorachivaniye are lost.