Originally Posted by
pennpaul
It's an Octalink bottom bracket and the cap is separate from the bolt.
That's the "self-extractor" part of the crank-fixing hardware. It's not actually necessary; the crank can be removed with a standard crank puller. There have been reports of this piece being cracked in the attempt to remove the crank by the self-extracting process. They do look nice though. I replaced mine with titanium from Toronto Cycles, sadly now apparently closed.
Split image. Top is original crank bolt and chainring hardware; bottom is the Ti replacement. Notice the original was not self-extracting.