Re: STUPID TURBO-DOWNPIPE BOLTS!! :MAD: (XSiVE)
The nuts are "interference fit". Imagine taking a normal nut and putting it into a vise and clamping down on it until it deforms a bit. Now you've got a slightly oval nut. The first few threads are circular, so it threads on normally at first, but once you are halfway into the nut or so, it starts to grab because the nut is slightly deformed.
Autotech sold me these with my exhaust studs - I think they were about $0.50 each. Had I been thinking, I would have bought 3 more for my downpipe as well.
(The nuts are copper, (copper plated at least), BTW)