Bolt dimensions help please?

I've managed to lose the rearmost bolt from my rear caliper, I can't get one online for a week to 10 days, there is an engineering dept here that might have something that will suffice though, can anyone tell me the dimensions of said bolt? I can find mention of it everywhere and part numbers but no length, thread or diameter

Any help would be much appreciated, could do with getting back on my bike as my wife needs her car back

[yorkie_chris]

Take the other one out and try it, then measure that one if it works. I have a feeling it may be an odd size though.

Yeah they both look entirely different
http://www.tastynuts.com/acatalog/TIRBMON150.jpg
the only similar looking thing is length, damn.
stupid pointies, least on the curvy there are two identical bolts but this just has to be different, grr.

Thanks for the suggestion though yc