This wooden divider board fits our horizontal top bar hives and top bar hive nucleus boxes (also called a follower board).
Follower boards create a false wall, indicating to a colony that they only have so much space to work within and cueing them to keep comb tidy and fill the space they have. As the colony expands and needs more space, the beekeeper can move the board, add a few bars, and therefore expand the hive.
My new top bar hive came with a single divider board. I decided to get a second one to put at the entrance end, covering the wing nuts and leg hardware. So far, so good. Bees come at the end of April so we shall see if my plan works.