Abstract: A fastening device includes a body having an engaging surface and threads concentric with the rotational axis of the body. The engaging surface has formed therein a plurality of ratchet-like projections having a sawtooth-type circumferential cross section. Each projection includes a first radially outer edge and a second radially inner edge which together define a leading point which forms a most prominent portion of the projection. Each first edge of each projection extends along a respective first tangent line of a plurality of first tangent lines which extend from an inner periphery to an outer periphery of the engaging surface in directions tangentially inclined with respect to the radial.

Abstract: A fastening device includes a body having an engaging surface and threads concentric with the rotational axis of the body. The engaging surface has formed therein a plurality of ratchet-like projections having a sawtooth-type circumferential cross-section. Each projection includes a first radially outer edge and a second radially inner edge which together define a leading point which forms a most prominent portion of the projection. All of the points are located on an imaginary circular line and facing in the direction of loosening of the fastening device. Each first edge extends outwardly from the circular line in a direction inclined to the radial, and each second edge extends inwardly from the circular line in a direction inclined to the radial. The circular line is positioned nearer the inner periphery of the engaging surface than the outer periphery thereof.