Our daycare had gotten a tractor and trailer for free but without the split to hold them together. I measured and designed my take on a split, trying out a print-in-place technique and it worked perfekt.  All you need extra is a spring. 

I printed it at 100% infill to make sure it was strong enough, especially the print-in-place part. Also print it horizontally as shown in the picture to get a better chance of the tiny rotating pin actually rotating and make the print stronger. It prints in about 7 hours plus 15 min for the spacer.