Lego Technic compatible X cross peg
thingiverse
My kid broke one of ours, and we didn't have a spare. It should be a tight-ish fit. They're not supposed to fall out. The peg has a slight round to the ends to help get it started in the hole.
Download Model from thingiverse
With this file you will be able to print Lego Technic compatible X cross peg with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Lego Technic compatible X cross peg.