It is used to connect a solid wire to an actuator arm, similar to a throttle arm on a carburator. The bolt is a special drilled AN3-4, which is 3/16" diameter, and 17/32" long. You would slide the bolt through the arm hole, slide the solid wire through the drilled hole in the bolt, and tighten the nut supplied to secure the solid wire at that location on the arm.

It has 10-32 threads.