one smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming

a slot is cut partly in middle of nut and then slot reduced by tightening screw

a hard fiber or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip

through slots are made at top and a cotter-pin is passed through these and a hole in the bolt, and cotter pin split and bent in reverse direction at the other end

on both the sides

on one side only

on none of the sides

may be provided anywhere

provide cooling action

lubricate the dies

help remove chips

all of the above

flaring

brazing

soft soldering

fusion welding

metric

buttress

square

NPT (national pipe threads).