PLEASE if you have the bolt size, post it here. Same damn thing happened to me Saturday night! Couldn't figure out what the hell the rattling noise was until I shocked myself by looking under the hood.
My mechanic has the car now and said he would get a new compressor clutch kit ($$$$$) but if I can instruct him to get a new bolt and reattach that would save me a lot of cash.
I've seen this reported several times now on several different forums and some folks have reported being able to source a replacement bolt from both hardware store stock and parts store shelves (not by part number, but from a nuts & bolts section), but so far not a single one has been kind enough to post a spec.