Recently changed my water pump, which means I had to take all the drive belts off. After a few days, the nut that holds the AC idler pulley fell off while I was driving.

1) What size is this nut and thread type?

2) The link below shows a blow up of this assembly. When I put this back on I only had 3 pieces; the collar (far left piece that says "discard" on page 2), the idler pulley, and the nut. This blow shows several other pieces. Am I missing something which would probably be the reason the nut came off? As I noted above, I did not even have a washer behind the nut...not sure if that is correct.

http://www.tegger.com/hondafaq/tsb/civic/x00-003e.pdf

 

Bueller?...Bueller? Anybody?

I got the nut that holds the pulley on, but still not sure if I'm missing a washer or anything else. TIA