the whole saw sizes

seven views, but no replies??

LOL, I'll go find out, and edit my post

for a 120mm I used a 4 1/2" hole saw, for the 80mm I used a 3: hole saw

You can go to google
type in:
convert 120mm to inches
convert 80mm to inches

this will give you your answer

Just get the compass tool for dremell's it is great for cutting holes.http://www.dremel.com/en-us/attachme...=69679&I=69820

 doesn't the hole saw have the diameter in mm right next to the inch-diameter? at least the ones in the nearby Lowes and Home Depot do

4 and 1/2 is not the size to use. You will make a hole that is slightly too small and make noise from the fan blades cavitation against the lip.

I use 4 3/4" and I use a rubber c channel. This makes the quietest/neatest hole in a side panel or top panel.