A "barb" is provided on the contact surface between the nut and washer, and it has a wedge structure that rotates in the tightening direction but does not rotate in the loosening direction. In addition, a protrusion is provided on the contact surface of the base material, and this protrusion bites into the base material to be tightened to prevent rotation. For these reasons, the nut will not loosen even in a harsh vibration environment (after 3000 cycles in the vibration type impact loosening test).
Furthermore, the washer is provided with a groove that matches only the dedicated jig (socket), and this jig is required to release the fastening, so it cannot be loosened with a normal tool.
Therefore, it is useful for preventing theft and tampering as well as preventing loosening.
Also, if you release it using a special jig, you can use it over and over again.