Beekeepers sometimes need to ventilate their hives. The trick is to create a small opening that's too big for the bees to plug up with propolis, but too small for them to use as an entrance/exit. The classic method is to glue popsicle sticks inside the outer cover of the hive (this is the "lid" of the hive - called an outer because there is a second inner cover to provide a way to exit the top of the hive). The problem with this is that the solution isn't reversible, requiring the keeper to have two outer covers. This thing is used in sets of two or four to lift up the cover just enough to ventilate the hive. Since it's removable, there's no need for a second cover! Update The new version has better dimensioning and is much less PLA hungry. I was worried about cover stability, but the larger version was just... larger, not more stable. I also added my 'maker's mark' to this version...