Check this out. My wife, on her way to work the other morning, ran over a flat bottomed (as in not sharp/pointy/screw-tipped) bolt that not only punctured her tire, it punctured her rim! Seriously! Through the rim tape and through the metal. And it went straight down, too. And the bolt had a rounded head. I can't even imagine how it would have been standing up, let alone her running it over just so perfectly as to embed it perfectly through the whole shebang. Boggles my brain. This was a B43 btw (thus making this post ss&fg qualified).