huh? I understand the concept of the star nut, but what I don't understand is the "round tube" into the "go-by" tube.. Please explain further..
"Go-by"...
When two elements, walls, tubes, etc. intersect, the joint is typically either a miter or a butt joint.
Here we have a butt joint in the drawing and on the cart.
One tube is butting and one tube is "going by".
The round tube...
In the drawing you can see how the connecting bolt could collapse the tube with too much applied torque especially with this thin-wall tubing on the cart.
The solution is to provide a stiffener (backing) to prevent this.
You would typically take a piece of round tube with an ID to allow the bolt to pass through.
You would also make the length lightly snug so it can be easily slid into position.
If you do this you will get a stronger joint, prevent collapse and be able to apply more torque.