ac compressor 5kq query

[geo <gamills@ns.sympatico.ca>]

I'm about to install the belt on the subject which I simply cut
off when installing the t-belt (winter doncha know).  The haynes
man. I have describes the procedure without details, and while I
was doing the prelim I noted there was a 'inni' hex bolt (allen
key type) that needs to be loosened on the bracket at the back of
the compressor (no help from the Haynes man. here - shows a
different bolt).  Can someone please tell me what size this is?
I don't have a big assortment of hex keys...yet.  I really hate
it when I go at something and don't have the right tool, end up
running around trying to find something that will work.  When I'm
lying on my back on the ground I want all the stuff I need right
there and ready to be grabbed.

any help appreciated...and the virtual ale/beer/toddy/etc. is on
me.

Geo