Hi all,
 
    one of the screws which used to mount the Unit is lose but I don't have a tool to fix it.  Which screw driver should I buy?  I noticed that the screw is something like octagon ?
 
Cheers!
Cowby 

Is it these here?
 
 
I believe you need a Torx bit, although, I'm unsure of the size. You'd probably need a set like this. 

Yes, joe is correct.  Those are Torx screws.  I use them all the time in my hobby,
and have done so for years.
 
Prices run all over the place.  You don't want to buy a very cheap set because
the tips will bend and chip and become useless quickly.  And there's no need to
spend $200. for a US made SK kit. (They are very nice, though.)
 
I think the best deal around for someone who won't use them often, but wants
high quality, is the Wiha.  They make excellent tools, mostly in Germany.
 
I'd recommend:
https://www.amazon.com/Wiha-36392-L-Wrench-Short-Piece/dp/B002QV0FGA/ref=sr_1_4?ie=UTF8&qid=1467448981&sr=8-4&keywords=wiha+torx+set
 
 
Cheers,

Yes, exactly the one I am talking about.  Will take a look the Torx.