I downloaded the directions and found that Nick didn't write, "U-clip - buy one at Home Depot." but rather he explained how to create a U-clip from a plain sheet of metal, or tin. He showed his trailers being used in a remote area of Nepal (no Home Depot there!), and he explains how even if a brand new metal cart was parachuted in, there'd be no where to repair the cart - maybe not even the hardware hitchers available that most of us take for granted when running out to get parts for our projects.
Great going, Nick! I hope to make you proud this summer. I've hybrided Nick's plans with an umbrella'ed lemonade stand. If you're in St. John's look for my cart and fall in love with my S-Move-Es by bike - first customers get a free umbrella in their drinks! I have sooo much to do! If you're looking to make a bike cart, here are two great sites I found: