Here is what is required
1) A M6 Allen bolt
2) A M8 allen bolt
3) 1/2 inch Steel or MS sphere/ball.
4) A neodymium ring magnet. I used a magnet with an ID of 6mm, OD of 20mm and 6mm thick.
To construct the joint, push the M6 bolt through the magnet, enough that it touched the head of the bolt. Place the steel ball on the side of the bolt where you place the allen wrench. Place the second M8 bolt on the steel ball.