Lowe, Price, LeBlanc & Becker
Loosening prevention screw
 The screw of this invention can be used for fastening members of a variety of materials and reliably prevent loosening of the screw. The screw shank is formed with two threads, a main thread for driving the screw and a sub-thread which extends in the same direction as the main thread, is smaller in outer diameter than the main thread and has a pitch different from the main thread. The inclination of the slant surface of the sub-thread is set steep on the loosening side and moderate on the fastening side. The pitch of the main thread is set larger than that of the sub-thread. When the tightened screw is applied a loosening torque, the sub-thread bites into the inner wall of the hole, preventing the screw from being loosened. 
Kabushiki Kaisha Suzuki Rashi Seisakusho
F F F F F
F16B F16B F16B F16B F16B
inventional inventional inventional inventional inventional
Yasuo
Suzuki