Relatedness?

I was won over watching Crout's KazooKeylele - Ukulele - The final countdown (hmmm... there's creativity for you) on YouTube, so I followed up... and watched Dorkbot Alba's Waldflöte vs Kazookeylele - dueling banjo's only to spot that Roundest Objects in the World Created was a "related" video. The latter is about incredibly precise spheres of silicon intended as possible replacements for the standard metric kilogram.

And the relationship is?