Same vent Cub Crafters uses in the sky light of their Carbon Cubs. Makes a lot of noise when you try to close it and it departs the airplane with part of the skylight. Always carry color coordinated duct tape. I use a 3" hole saw in the drill press turned slow to drill the hole because, like noted above, the vents don't work well if the hole is wallowed out from a chattering hole saw.
I have had both the big ones on the roof of the cub crafters and 2" snap vents on my Husky. The Husky vents are at the lower corner of the side windows.
The 2" ones on the husky cost $15 a pair and are far superior in performance and ease of use. http://snapventplastics.com/snapvent-ventilators/a-2-100/