Abstract: A tamper-proof, self activating nut lock apparatus comprises a threaded shank having an external screw thread of a first pitch and a coaxial threaded bore at one end of the threaded shank, with an internal screw thread of a second pitch, both the said external and internal screw threads having a same direction of rotation. A shank extension having the external pitch of the first pitch and a coaxial threaded projection of the second pitch is screwed into the threaded bore of the shank and a threaded nut is adapted to engage the external threads of the shank and the shank extension. A friction means, such as a nylon insert, is adapted to engage the shank extension and the threaded nut whereby reverse rotation of the nut to remove the nut from the shank without appropriate tools rotates the shank extension for jamming the nut on the threaded shank to prevent removal of the nut.