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So I jacked up the front end of my truck to put some half round spring rubbers in. The truck took a direct hit from a dust devil and cause the truck to wobble off the jack. The bumper came down and hit me in the neck. I'm lucky I decided to leave the tire on otherwise the bumper would have crushed my neck.
That is why I use a jack in combination with the jack stands. I keep all the weight on the jack stands and use the jack as a 3rd point to stabilize it, usually in the middle.