grabcad
I created this for a request by Nick Van Laar:
http://grabcad.com/requests/universal-joint
It is based completely on the picture he provided (and the very little knowledge I have of u-joints)... I hope this fits his need.
**EDIT** I updated the model to include the retainer cups and snap rings.
Direct link to the original creator's page
Click the "View on grabcad" button above to visit the original model page on grabcad. You can download the STL file directly from the creator's page for free.
This STL file is compatible with most FDM 3D printers (Creality Ender 3, Prusa MK3S+, Bambu Lab, etc.) and resin printers (Elegoo, Anycubic). Check the original page for recommended print settings and materials.
Yes, this model is available as a free download on grabcad. Some creators accept tips or donations.
Most STL files can be modified using free software like Blender, TinkerCAD, or Meshmixer. Check the license on the original grabcad page to see if modifications are permitted by the creator.