Blakbird, I followed the link for the tubing you used on the Marble Run. Unfortunately, tubing sizes, lengths, etc is a weak point of mine. I get thoroughly confused with metrics. I'm attaching a link to the part of the page with the different sizes to which you pointed. I would sure appreciate it if you would be kind enough to point out which tubing you ordered? I've gathered all the parts necessary to assemble it sans the tubing. Thanks in advance for the information in particular and for all the work you've put into creating the instructions for Akiyuki's models!!
https://www.mcmaster.com/#catalog/122/140/=10ycofo