Self-locking fastening device

A fastening device comprising:

• a body having a rotational axis, an engaging surface and threads concentric with said axis;
• said engaging surface having formed therein and extending therefrom a plurality of ratchet-like projections having a sawtooth-type circumferential cross section;
• each said projection including a first radially outer edge and a second radially inner edge which together define a leading point which forms a most prominent portion of said projection;
• all of said leading points facing in the direction of loosening of the fastening device;
• each said first edge of each said projection extending along a respective first tangent line of a plurality of first tangent lines which extend from an inner periphery to an outer periphery of said engaging surface in directions tangentially inclined with respect to the radial;
• each said second edge of each said projection extending along a respective second tangent line of a plurality of second tangent lines which extend from said inner periphery to said outer periphery of said engaging surface in directions tangentially inclined with respect to the radial and in a direction of inclination opposite to that of said first tangent lines;
• and
• said first tangent lines and said second tangent lines being spaced at regular intervals such that each said first tangent line intersects a plurality of said second tangent lines, and such that each said second tangent line intersects a plurality of said first tangent lines, thereby forming a plurality of said leading points along each said tangent line between said inner and outer peripheries of said engaging surface.