For Bee keeping

Steher nucleus box (Simplex dimention) -> flight opening reduction

Dimentions of the opening of Steher nucleus "Simplex": 15 x 1 cm total

Opening for bee's to pass: 4,2- 4,4 mm (blocks also Vespa Velutina/yellow legged hornet to enter)

Reduces the opening with 1 or 2 thirds iff wanted - prevents robbing

Can be uploaded in a CAD editor and easily made wider/more narrow for other standards than Simplex

Tested - worked fine (I printed it with no supports)