Where the three bolts that go through the three u-brackets on each leaf, there is a tube that the bolt goes through. I guess as the leaves flatten it makes the pipe roll rather than wear on the bolts.

A day without laughter is a day wasted- Charlie Chaplin
When wrestling a grizzly bear, you have to keep at it until the bear gets tired, not when you get tired.
1948 Chevy 2-Ton