Originally Posted by CattleRustler

all I am saying is a holesaw is far superior for cutting fan holes as opposed to a dremel or a jigsaw.

Bi-Metal holesaws
for 120mm use 4 1/2"
for 140mm use 5 or 5 1/4"

bi-metal holesaws wont dull after 2 cuts when used correctly. Apply some tapping fluid to the teeth before you cut case metal and the saw will last a good long time. I have holesaws that I used to cut case steel, plate steel, steel bar, and tempered aluminum, and they arent dull at all. For thin metals I used tapping fluid to coat the teeth. For thicker metals I used dark cutting fluid. All of this is available at home depot / lowes / mom and pop hardware.

Originally Posted by Theodore Roosevelt