Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4094231.
This itty-bitty super fast print makes it incredibly simple to assemble Traxxas style heim-joints/balljoints/rod-ends/whatever you want to call them.
All you need to do is press an M3 nut into the recess and use an M3 bolt through the ball, then the joint, then this tool into the nut. Anything 18mm or longer will work. It takes almost zero effort to press the balls into the joints with this tool, and it's very quick to take back apart and set up the next one.
I hope this helps someone. :)
I uploaded a picture taken from FreeCAD so you can see what it looks like, as it seems Thingiverse is having trouble rendering the STL (too small?).
Also, FWIW: I wouldn't bother with the Traxxas style press-in joints from Aliexpress for a delta-printer. Far too much play. They were cheap and I thought I'd try 'em. I may find some non-3D printer related project that needs them.