thing to do is to make a mark to know were to cut the blowhole.
The best way to do this is to use your fan as a template. This
will give you the exact measures. You can tape the fan at its
place to make sure it doesn't move. Don't forget to mark your
make your blowhole, you'll need some kind of cutting tool. A
good jigsaw with metal blade will give you the best results,
but I used a hand powered metal cutter. You'll also need a drill
to make the screw holes. When you're done, it should look like