To provide a method that fixes a bolt and a nut to an arbitrary position with a pin because when the bolt and the nut are used in vibration of a machine for a long term, loosening occurs and the nut may be removed.

In an arbitrary lock nut, a U-shaped type groove 3 having a width twice as large as a groove 4 of a nut 2 is formed in the thread part of a bolt 1 so as to be parallel with a rotation shaft, and many grooves with equal intervals are formed in the inner diameter part of the nut 2 so as to be vertical to a thread. The arbitrary lock nut fits a pin 5 to the groove of the bolt and inserts the pin 5 into the groove of the nut, to thereby stop rotation.