This slotted steel excluder can be used on our poly nuc hive range meaning you have full control where the queen can lay. Do you give her access to all or one of the brood extensions? are you going to use the super extension for her to laying in or would you rather collect honey instead? This opens up the possibility of using the poly nuc as a lightweight but fully working honey production hive, or just a regular nuc box. For use with the BS Poly Nuc, not suitable for the langstroth size nuc.