Elastic nut is a locking device in which

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 fibre 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

Please do not use chat terms. Example: avoid using "grt" instead of "great".