Simply attach with a screw in the center to cover a drilled hole in your NUC box. This 5" wide galvanized steel entrance reducer disc has 3 settings:
1.) Closed with Vents
2.) Queen/Drone Excluder
3. Free Access Simply. This open setting is approximately 1.75" across.
These really are worth purchasing for your nucs rather than a traditional entrance. If you ever need to move them you just spin in around and now it's closed. Last year I had some robbing issues and this year I'm glad I will have the ability to just close up my nucs and move them if needed.