Screw with groove for self-lock and method and rolling flat die for manufacturing the same

A self-locking screw having a longitudinal axis and comprising a thread having an inner radial portion and an outer radial portion, said inner radial portion having a pair of opposite first side faces defining a flank angle of said screw, said first side faces each being disposed at an acute angle relative to said axis, said outer radial portion having a pair of opposite second side faces extending from said first side faces, said outer radial portion also having first and second outer radial faces extending respectively from said pair of opposite second side faces, said pair of second side faces being generally planar surfaces which are parallel to one another and which are perpendicular to said axis, said pair of second side faces having outer radial terminating ends, said first and second outer radial faces extending from said terminating ends and being disposed generally parallel to said axis, said thread having a central groove means defined by a radially inwardly extending buffer groove having two groove side walls and a bottom juncture means joining said two groove side walls at the innermost radial end of said two groove side walls, said two groove side walls each having an outer radial terminating end joined respectively to said first and second outer radial faces such that said two groove side walls extend generally radially inwardly from said first and second outer radial faces, said two groove side walls along with said second side faces and said first and second outer radial faces defining two axially spaced elastically deformable thread portions which are elastically deformable such that as said thread is threaded onto a counterpart threaded member, said elastically deformable thread portions are engaged by said counterpart threaded member and elastically deformed as said thread portions axially approach one another and reduce said axial spacing between said thread portions, said inner radial portion of said thread being rigid to retain its initial configuration after having been threaded onto said threaded counterpart, whereby said outer and inner radial portions provide the elasticity and rigidity to obtain a high tightening force while resisting loosening thereof.