This 2 inch wide entrance reducer disc has 3 settings.
1.) Closed with Vents
2.) Queen/Drone Excluder
3. Free Access Simply attach with a screw in the center to cover a drilled hole in your nuc box.
These are a lot smaller than the large metal discs. I use them on my queen mating boxes/castles. The queens have no problem returning from mating flights and finding their entrances. These will certainly work for regular nuc entrances as well.