Are you running the new Rotor track spider, these are the spare chainring bolts you will need. The spiders are not designed to nut the tradition two piece nut bolt system., so no point steal one off your mates bike.
Threaded directly into the spider, m10 thread for a 6mm Allen key, no back nut.
These bolts are only compatible with Rotor ALDHU Track and VEGAST Track cranksets.