A Slatted Rack is installed between the bottom board and the bottom brood chamber. In the fall, it keeps the brood chamber warmer so the queen can lay right to the bottom of the frame. In the spring and summer, when hive populations are at their largest, it provides a cluster space in the hive which can reduce swarming. Slats run perpendicular to the entrance. Fully assembled. Choose 8 or 10 frame hive.