Ball-links must be flexible but adequately rigid. The threaded part of the rod cuts its own thread in the ball-link, and no further fixing is necessary. Use silicone oil, Order No. 10/37, for maintenance.
How do you know when the pushrod meets the end of the socket, and does it becomes screwed to far into the ball-link accidentially? These ball-links feature a check slot, so you just screw in the pushrod until the end is visible.