A. one small nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
B. a slot is cut partly in middle of nut and then slot reduced by tightening a screw
C. hard fiber or nylon cotter is recessed in the nut and becomes threaded as the nut is stewed on the bolt causing a tight grip
D. 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