Ask any mechanic, and they probably have a drawer or box full of old nuts and bolts. It may not be very often that they need to be rummaged through, but sometimes they can solve problems.
I was replacing part of the exhaust on my Corolla and was having trouble getting the muffler reattached. In the process I cross threaded one of the spring bolts. Luckily, I used to work at a Toyota dealership and kept some old exhaust spring bolts from my time there, and had exactly what I needed.
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