The bolt was a tru-value hardware store M5 I think, I was on a flat bike path and although I was a bit shaken I did look in the immediate area for the bolt assuming if it had come off as a result of the crash I would see it, I did not find it. I didn't do a hard target search but it wasn't lying near the bike. I would like to think the rack was adequately secured to the bike but seeing as the rack was loose it seems like the most likely scenario was the bolt came off.