To answer a few of the questions. The seat post is a suspension post that came with the Cannondale. The bolt goes up through the mount on the post through the clamp. It is(was) quite tight as any loosening allows the saddle to shift positions. The bolt fails at the bottom of the upper clamp. This is the third time I've had one fail. First time I was only a mile or so from a hardware store, Second time I had a spare with me. This time, as I said, the upper clamp and the broken bolt section, fell in the grass along the bike path, and disappeared, so my spare bolt was useless. My best guess is about 8000 miles between failures, so not something I worry all that much about. Probably should be a hardened aircraft grade bolt but they're not easily available at the local Ace.
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