After I made some holes in my kitchen for the fridge to ventilate trough I realized that it looks pretty ugly. I came up with these vents to do the trick. They  slide in easily into the holes, but they wont came out easily due to an anchor mechanism. You can remove them with a firm pull though. 

Hole size

Depth: 18mm

Diameter: 67mm

You can resize the model to fit different sized holes too.

For example: Depth 30, Diameter 100

  30/18   = 1.667 → Resize height to 166.7%

  100/67 = 1.493 → Resize length and width to 149.3%

If the ratio of these parameters are very different from the original the model might become distorted.