Closure assembly having a deformable anti-backoff feature independent of the screw threads

An anti-backoff closure assembly, comprising:

• a container having a neck portion extending therefrom, said neck portion forming an opening and having at least one first protrusion and at least one screw thread on an outer surface of said neck portion, wherein said at least one first protrusion is independent of said at least one screw thread;
• and
• a cap having on an inner surface at least one second protrusion, at least one groove independent of said at least one second protrusion, and a seal for releasably engaging said opening of said neck portion to form a leak free seal, wherein said at least one first protrusion and at least one second protrusion engage to create an interference fit when said at least one screw thread and said at least one groove are threadably engaged, upon engagement said at least one second protrusion deforms said at least one first protrusion sufficiently to form an indentation on said at least one first protrusion that resists backoff as the pressure between said at least one screw thread and said at least one groove is reduced as a result of plastic relaxation, thereby maintaining said leak free seal of said seal within said opening.