One small nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
Hard fibre or nylon cotter is recessed in the nut and becomes threaded as the nut is stewed on the bolt causing a tight grip
A slot is cut partly in middle of nut and then slot reduced by tightening a screw
Through slots are made at top and a cotter pin is passed through these and a hole in the bolt, and cotter pin splitted and bent in reverse direction at other end
EXAMIANS