An extension bar for a ball-and-socket joint. Created to move the phone closer to the user from the windscreen mount, but it can be used anywhere there's a ball-and-socket joint. It can be resized 120mm to over 180mm and locked into place.
Print in ABS or PETG or similar, so it survives inside a car in the summer.
You need a 25mm M3 bolt to strengthen the neck; the first print failed very quickly there.
The OpenScad source requires the STLs from the Open Source Ball Joint, but since that's an 18mm ball and I needed 20mm, it's resized to suit. The extension bar is sized to match the end-faces of the resized STLs. If you want a longer or shorter bar, alter the connBot/connTop in the source.
The author remixed this model.

This is an extension bar for the Ball Joint. The scad source uses and resizes its STLs.
The thread library was used for the thread/nut to lock the two parts together.