I made this Universal Joint for an RC car I'm working on. It runs on a 3d printed 8mm keyed shaft. A picture is included to help you recreate a driveshaft that fits your desired length. I also included a 30mm shaft to help get you started. I designed it to be printable and then post-processed to achieve free movement, but I've decided to expand the tolerances instead. You may still have to drill the holes to get a good fit. I recommend printing with PETG for extra flexibility when snapping it onto the center. The center can be whatever material, but I'd still recommend PETG.