I just took the gas tank off the car (pinhole leak, new one arrives this week from discountgastanks.com. . .i'll let everyone know the quality). I Noticed that the bolts have a spiral pattern cut into them across the threads. (No, i am NOT talking about the threads themselves) This spiral probably has three turns over the length of the bolt. The splash pan bolts had the same thing. Is there a reason for this? Feel free to make something up if you don't know. It's going to be a slow day at work tomorrow and i need to be entertained.

Those flutes act as thread cutters. As Art said, they'll cut through any overspray that occurs during manufacturing so the bolts will have metal-to-metal contact. This helps to keep the tank grounded.

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Don Foster (near Cape Cod, MA)

The flutes clean out excess paint or corrosion inhibitor applied to body weld nuts before assembly.
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Art Benstein near Baltimore