Rod End Ball-Joint M6 : High strength / Low clearance Balljoint

Higher strength design
Uses two metal nuts to bear the axial forces, instead of a weak plastic thread which would be liable to creep and loosen.

Lower clearance 
The design has a takeup feature so that when the hatch (lid) is fitted it exerts a slight force against the ball. The ball then feels a bit tighter to rotate, but free play is removed.

Printing
The print-in-place ball has nominal clearance of 0.3 mm per side. Mine were seized when printed, but a few gentle taps of the mallet got them free (see photo).

Clearance adjustment
The hatch can be tight to fit but should ease into place without excessive pressure. If it's too tight to shut fully, then you can carefully remove material from the spring-fingers of the hatch (see image) until the hatch shuts with the correct tightness.
If the amount of free play is not important then you can even snip off part of the spring device.

Fasteners
Use M6 threaded rod and 2 off M6 DIN nuts which are each 4.9 mm tall. It's important to use the correct type.
To fasten the hatch use 3 off woodscrews, Ø3 mm; length 10 - 15 mm.

If fastening the ball (eye) using an M6 bolt then you might need to size the eye hole by drilling or reaming.

Length adjustment
Cut the threaded rod about 22 mm short of the eye centre (per rod end). 
Example: for a double-ended linkage, if the eye-to-eye distance is 300 mm then cut 256 mm of threaded rod.   300 - 2 x 22  =  256
You can fit the linkage into place without the hatch, and adjust the nut positions to get them right. 
When done, tighten the pair of nuts against each other, and enclose with the hatch piece.

▲ Safety notice
Although this is a good strong design for what it is, it's still a printed plastic item and should not be relied on for applications where failure might cause injury. In such cases use a reputable steel balljoint with appropriate strength rating.

═════  Update 2023-11-27  ═════

The latest models (date suffix 20231124) have the following changes : 

1. Adding a fillet around the housing (green highlight in image)
   
    
2. Adding auxiliary spacer which matches the integrated spacer of the ball
   
    
3. FreeCAD source model here includes other components which have their own Printables pages (find the STLs, photos and descriptions there)…
   
   ► Surface mount pivot bracket   https://www.printables.com/model/661542 
   
   ► Kitchen drawer brace bracket  https://www.printables.com/model/661836