Contraptor

I've got two things on my mind for this.

The U channel seems sort of tricky to get (I'll obviously break down and put in an order for it a McMaster if I can't find it locally). Is there another name for it or other materials that work?

Second, what is the experience with longevity. My intuition is suggesting that the sliding elements might need a lot of adjustment. Any reports on that?

Either way, I'll very likely use them on my first Contraptor since they clearly are simple and inexpensive.