What is a lug nut?

This is a lug nut.

What does it do? It keeps this from happening:

The Parable of the lug nut

Once upon a time there was an old man, a grandpa to a bunch of kids who relied on him to keep them entertained. One day, while Grandpa was resting in the early winter sun, smoking his pipe and thinking about some weighty problem (as that was the kind of guy he was), one of the kids ran up to him and cried; “Grandpa! One of your tires has gone flat on your old truck!”

“Oh hell,” thought Grandpa as he went to the barn to get his equipment, which he then loaded onto a wagon and headed down the path to where his old truck was parked. He was followed by a gaggle of kids, who were all keyed up and full of wonder and questions.

“What’s that for? Why is it flat? How will you fix it?” Each question answered with thoughtfulness and patience.

“This is a hydraulic jack that raises the frame up so I can work on the wheel. I don’t know yet why it is flat, but once it’s off I can do the bubble test. First I’ll use that cross-shaped wrench, called a lug wrench, to remove the lug nuts,” He said as he began to jack up the heavy truck.

“Lug nuts? What are lug nuts?” one of the kids asked.

“See these? These are lug nuts. They hold the wheels onto the axle and I have to remove them to look for a puncture in the tire,” Grandpa said.

“Actually, there’s a story about lug nuts that I could tell you while I’m struggling to get these nuts loose, would you like to hear it?” asked Grandpa.

“Sure! Let’s hear it!”

“Okay gather around, but not too close, we don’t want an accident, do we!”

The kids shook their heads and looked around their ranks to see if anyone looked like they wanted to get into some mischief. Nobody stood out so they all quieted down and got ready for the story.

“Once, a long, long time ago, before automobiles were invented, when wagons owned the roads (for what was a wagon but an automobile without a motor).  In fact many components on those wagons evolved into auto parts, like the steering wheel and the lug nuts!