This is a Prop Balancing Rod for Self-Tightening Propellers on DJI aircraft, such as the Phantom 3, Phantom 2, Phantom 2 Vision, and Vision+ Plus Quadcopters. One end has right-hand threads, and the other has left-hand threads. This is perfect for use with the Dubro Tru-Spin Prop Balancer.
Balancer and prop shown in second image are for illustration only. The DuBro balancer is available separately below.