This is an isolator for a HF wire antenna. There is a double D slot for a banana plug, holes to thread a rope through and a set of small holes to thread the wire through.

Loop the rope over and under through the holes and tie a slip knot. This will allow you to adjust tension on the rope. There are some vertical edges to help stabilize the rope.

Feed about 6-10 inches of wire through the front small hole, over and under the left or right hole, over to the opposite hole, and finally over or under and back through the front hole. Wrap the wire in a half western union and run the remaining pigtail over to the banana jack solder lug, wrap it around, and solder it. You may also solder the half western union if you wish but that should not be needed.

If you use aluminum wire then I would suggest crimping a ring terminal on the end of the wire and skipping the half western union. Sharp turns on aluminum are bad. Swaying will quickly fatigue the wire if you make any sharp angles. Friction should hold the aluminum in place and a large sweeping arc back to the terminal would be advisable.