One tool every gearhead should have and why

I really like my Dewalt 1/4 impact driver. Small, compact. Li-ion battery kicks like a mule. Darn thing can put down 125ft/lbs of torque! But I use it mainly to remove nuts. I also had a 12" 1/2-9/16 combo box end wrench that I liked so much I wore it out.
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